NANYANG JUNIOR COLLEGE JC 1 PROMOTIONAL EXAMINATION Higher 2
CHEMISTRY
9647/01
Paper 1 Multiple Choice
11 Oct October ober 2010 2010 1hour
Additional Materials:
Multiple Choice Answer Sheet Data Booklet
READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, highlighters, glue or correction fluid. Write your name, CT and NRIC / FIN on the t he Answer Sheet in the spaces provided.
There are forty questions forty questions in this paper. Answer all questions. For each question there are four possible answers A answers A,, B , C and D. Choose the on e you consider correct and record r ecord your choice in soft pencil on pencil on the separate answer sheet.
Read the instructions on the Multiple Choice Answer Sheet carefully.
Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should should be done in this booklet. You may use a calculator.
This document consists of 12 printed 12 printed pages.
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2 Section A For each question in this section, there are four possible answers, A, B , C, and D. Choose the one you consider to be correct. Use of the Data Booklet is relevant to this question.
1.
How many molecules are present in 1 cm3 of oxygen gas under room conditions?
A
1 x 24000__ 6.02 x 1023 B 1 x 6.02 x 1023 24 000 C 1 x 6.02 x 1023 x 32 D 6.02 x 1023 x 24 000 1 x 1 000
nO2 =
1 24 ×1000
no.ofmolecules = 2.
1 24 ×1000
× 6.02 ×10 23
The reaction of hydrogen sulphide with sulphur dioxide gives sulphur as one of the products. H2S (g) → S (s) + 2H+ (aq) + 2eSO2 (g) + 4H+ (aq) + 4e- → S (s) + 2H2O (l) How many moles of hydrogen sulphide are needed to react with SO 2 to produce 1 mole of sulphur? A B C D
3/2 mol 1/3 mol 2/3 mol 2 mol
overall equation: 2 H2S + SO2 → 3 S + 2 H2O n H 2S 2 2 2 = Hence nH2S required = ×1 = nS 3 3 3 3.
In an experiment, 10 cm3 of a solution containing a known concentration of iodate (V), IO3- ions was run into an acidified solution containing an excess of iodide ions. The iodine liberated was found on titration to react with exactly 30 cm3 of 0.1 moldm-3 of sodium thiosulphate solution. The equations concerned are IO3- (aq) + 5I- (aq) + 6H+ (aq) → 3H2O (l) + 3I2 (aq) 2S2O32- (aq) + I2 (aq) → S4O62- (aq) + 2I- (aq) The concentration of the iodate (V) ions was 9647/01 NYJC Promotional Exam 2010
3 A B C D n I 2 nS O 2− 2
3
0.02 mol dm-3 0.05 mol dm-3 0.10 mol dm-3 0.15 mol dm-3
1 n IO3− 1 = , = 2 n I 2 3 1
∴ n IO − = nS O 3
=
1 30
0.1 = 0.0005mol 6 2 6 1000 0.005 [ IO3− ] = = 0.05moldm −3 10 2− 3
1000 4.
Use of the data Booklet is relevant to this question. Some isotopes are unstable and decompose naturally. In one type of decomposition, a neutron in the nucleus decomposes to form a proton, which is retained in the nucleus, and an electron, which is expelled from the atom. Which change describes a process of this sort? A B C D
1 0
11
C 12C 22 Na 22Ne 32 P 31P 40 K 40Ca
n → 11 p +
0
−1 e
(expelled)
Overall, mass number remains the same (options A and C are eliminated), while proton number increases by 1 (only D is correct). 5.
Which one of the following sets of elements includes a giant metallic structure, a macromolecular structure and a simple molecular structure? A
Na, C, Hg
B
Mg, Si, C
C
Si, C, H
D
Al, Si, S
A – Na, Hg: Metallic, C: Macromolecular B – Mg: Metallic, Si, C: Macromolecular C – C, Si: Macromolecular, H: Simple molecular structure D – Al: Metallic, Si: Macromolecular, S: Simple molecular structure
6.
Which of the following compound is expected to have the lowest boiling point? A
H2O
B
H2S
C
H2Te
D H2Se
Hydrogen bonds between H 2O molecules is stronger than van der Waal’s forces present between H2S, H2Te and H2Se molecules hence H2O has the highest boiling point. Amongst H2S, H2Te and H2Se, H2S has the lowest boiling point as strength of vdw increases with increasing Mr . 9647/01 NYJC Promotional Exam 2010
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4 7.
Which of the following pair of molecules have the same shape? A B C D
BeCl2 CO2 XeF4 NH3
NO2 SO2 CCl4 PCl3
A – BeCl2: linear (2bp, 2lp), NO2 bent (2bp, 1lp) B – CO2: linear (2bp, 0lp), SO2: bent (2bp, 1lp) C – XeF4: square planar (4bp, 2lp), CCl4: Tetrahedral (4bp, 0lp) D – NH3, PCl3: trigonal pyramidal (3bp, 1lp) 8.
Solid X has the following properties. i. It is insoluble in CCl4 and water. ii. It melts at 501 oC. iii. It is a non-conductor of electricity. Which of the following is a likely identity for X? A
Lead Chloride
B
Iodine
C
Diamond
D Barium
A – PbCl2 is an insoluble salt and as it is a solid, it cannot conduct electricity as the ions are held in fixed position in the solid lattice. B – I2 is a non-polar molecule should be soluble in non-polar solvent CCl4. C – Diamond should have a very high melting point as a lot of energy is required to break the strong covalent bonds between the atoms. D – Ba conducts electricity as the delocalized electrons can act as mobile charge carriers. 9.
A 2 g sample of hydrogen at temperature T and of volume V exerts a pressure p. Deuterium, 21H, is an isotope of hydrogen. Which of the following would also exert a pressure p at the same temperature T ? 2 g of deuterium of Volume V V 4 g of deuterium of volume 2 C A mixture of 1 g of hydrogen and 2 g of deuterium of total volume V D A mixture of 2 g of hydrogen and 1 g of deuterium of total volume 2 V
A B
4 g of D2 = 1 mol of D2, 2 g of H2 = 1 mol of H2. The original sample contains 1 mol of gas particles and exerts a pressure of p. In option C, the mixture of 1 g of H2 and 2 g of D2 amounts to 1 mol of gas particles as well, hence will also exert p. 1 A: pressure = p 2 B: pressure = 2 p 5 D: pressure = p 8 9647/01 NYJC Promotional Exam 2010
5 10.
Which of the following exerts the highest pressure? A B C D
1 mol of N2 at 0 o C in 11.2 dm3 1 mol of N2 at 27 o C in 22.4 dm3 1 mol of H2O at 27 o C in 11.2 dm3 1 mol of H2O at 77 o C in 22.4 dm3
Using PV=nRT, 1 x 8.31 x 273 5 = A: P = 2.02 x 10 Pa 11.2 1000
B: P =
1 x 8.31 x 300 22.4 1000
= 1.11 x 105 Pa
C & D: H2O is a liquid at the given conditions.
11.
Which of the equations correctly represents standard enthalpy change of atomization of iodine ? A B
½ I2 (s) ½ I2 (g)
→ →
I (g) I (g)
C I2 (s) D I2 (g)
→ →
2 I (g) 2 I (g)
Under standard conditions, iodine is a solid 12.
Which of the following enthalpy changes has a negative value ? A B
Na (g) Cl2 (g)
→ →
Na+ (g) + e2 Cl (g)
+ C NaCl (s) → Na (g) + Cl (g) D Cl (g) + e- → Cl- (g)
Although some electron affinity values can be positive, in this question, options A, B and C are endothermic. 13.
Which value would be required to estimate the lattice energy for the hypothetical ionic compound MgH ? A B C D
The first ionization energy of hydrogen. The electron affinity of hydrogen. The second ionization of magnesium. The magnesium-hydrogen bond energy
MgH consists of Mg+ and Hfi ions.
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6 14. A student used the apparatus below to heat a can containing 300 g of water.
thermometer can containing 300 g of water
burner containing propan-1-ol The following data were recorded: Mass of propan-1-ol burnt Change in temperature of water You are given that: Relative molecular mass of propan-1-ol Enthalpy change of combustion of propan-1-ol Specific heat capacity of water
= m g = ΔT oC = 60.0 = −2021 kJ mol−1 = c kJ kg−1 K−1
What is the efficiency of this heating process? m × 2021× 1000
A
300 × c × ΔT × 60.0 m × c × ΔT × 60.0
B
300 × 2021× 1000
× 100%
× 100%
C
300 × c × ΔT × 60.0 × 100% m × 2021
D
300 × c × ΔT × 60.0 × 100% m × 2021× 1000
Heat evolved by burning propanol = m/60.0 x 2021 x E/100 kJ where E is the efficiency of the heating process heat absorbed by water in can = 300 x c/1000 x ΔT kJ equating the heat changes will give D 15.
Production of ammonia is an important industrial process. The reaction proceeds via the following equilibrium. N2(g) + 3H2(g)
2NH3(g)
θ
ΔH
= -92.2 kJmol-1 ; ΔSθ = -197 JK-1mol-1
Assuming that ΔH and ΔS do not change with temperature, which of the following statements is correct? The equilibrium position shifts to the right only at temperatures greater than 195oC. B The equilibrium position shifts to the left only at temperatures greater than 195oC. C The equilibrium position shifts to the right only at temperatures greater than 468oC D The equilibrium position shifts to the left only at temperatures greater than 468oC.
A
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7 At equilibrium,
ΔGθ = 0 ⇒ ΔH θ = T ΔS θ −197 −92.2 = T ⇒ T = 468 K = 195 o C 1000
At T>195oC, the endothermic reaction is favoured, i.e. the backward reaction. Hence POE shifts left. 16.
Which of the following statements describe the melting process of ice at room temperature. A B C D
It is exothermic and its ∆S has a positive sign. It is exothermic and its ∆S has a negative sign. It is endothermic and its ∆S has a positive sign. It is endothermic and its ∆S has a negative sign.
Melting is an endothermic process and entropy increases as S(l)>S(s). 17.
Why does the endothermic reaction NaHCO3 (s) + HCl (aq) → NaCl (aq) + H2O (l) + CO2 (g) occur spontaneously at room temperature?
∆H>0
A NaCl has stronger ionic bonds compared to NaHCO3. B The endothermic enthalpy is compensated by the dissolution of NaCl. C The endothermic enthalpy is compensated by the strongly exothermic bond formation of carbon dioxide and water. D There is an increase in disorder. ∆G
= ∆H - T∆S. Since ∆H is negative, for the reaction to be spontaneous at room temperature i.e. ∆G is negative, it has to be that ∆S is very positive. Hence D is the best option. 18. A sample of gas was placed in an empty container at a certain temperature,
T o C and the percentage of products at equilibrium was measured at various pressures. The experiment was repeated for the same sample of gas, but this time at a higher temperature of (T + a) o C . The results are plotted graphically below.
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8 % of products at equilibrium
(T + a) o C T oC Pressure Which of the following equilibria is the sample of gas likely to be? A B C D
N2 (g) + 3H2 (g) 2NH3 (g) ; ΔH = -92 kJ mol-1 3O2 (g) + 4NH3 (g) 2N2 (g)+ 6H2O (l) ; ΔH = -1248 kJ mol-1 2N2 (g) + O2 (g) 2N2O (g) ; ΔH = +82 kJ mol-1 CO2 (g) + C (s) 2CO (g) ; ΔH = +173 kJ mol-1
High temperature favors forward reaction, hence the reaction must be endothermic reaction. High pressure favors backward reaction, hence the reaction must have less gas reactants than products. 19. At 350 o C , 50% of 1 mole of dinitrogen tetroxide dissociates according to the
equation: N2O4 (g) 2NO2 (g) If the equilibrium pressure is 100 kPa, what is the equilibrium constant, Kp for the reaction at 350 o C ? A B
C
100 kPa 3 200 kPa 3
D
N2O4 (g) 2NO2 (g) i/mol 1.0 0 c/mol -0.5 +1.0 e/mol 0.5 1.0 0.5 PN2O4 = x 100 kPa 1.5 1.0 PNO2 = x 100 kPa 1.5
300 kPa 4 400 kPa 3
2
⎛ 200 ⎞ ⎜ 3 ⎟ ⎠ = 400 kPa KP = ⎝
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100 3
3
9 20.
PCl5 undergoes the following dissociation, PCl5 (g) PCl3 (g) + Cl2 (g). At equilibrium, the number of moles of PCl5 , PCl3 and Cl2 are 0.09, 0.03 and 0.03 respectively. When 0.07 moles of Cl2 is injected into the system, what is the new equilibrium amount of Cl2? A B
Less than 0.03 moles Between 0.03 and 0.10 moles
C 0.10 moles D Greater than 0.10 moles
When 0.07 moles of Cl2 is added, the amount of Cl2 increases, i.e. more than 0.03 moles of Cl2 will be present. By Le Chatelier’s principle, the equilibrium will shift to the left so as to reduce the change that is imposed onto the system. In so doing, amount of Cl2 will drop, i.e. less than 0.10 moles will be present at new equilibrium. 21.
Which of the following graphs describes the kinetics of an enzyme-catalysed reaction against temperature? A rate
temperature
B rate
temperature C
rate
temperature D
rate
temperature With increase in temperature, rate increases to a maximum until the enzymes are denatured, and will not work anymore, hence rate will then decrease.
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10 22.
The diagram shows the Boltzmann distribution of the speeds of the molecules of a gas. Point X represents the most probable speed. If the gas is cooled, in which direction does X move? s e l u c e l o m f o n o i t r o p o r P
D X
C B
A
Molecular Speed ANS D When temperature is lowered, the proportion of molecules with lower speed will increase (graph will shift to the left, top) such that so that the overall area is still conserved (because the area under the graph represents the t otal number of molecules). 23.
Nitrogen monoxide, NO, reacts with ozone, O3, to produce nitrogen dioxide, NO2, and oxygen, O2, NO (g) + O3 (g) → NO2 (g) + O2 (g) For the proposed mechanism below, which species are intermediates? (1) (2)
O3(g) → O2(g) + O(g) NO(g) + O(g) → NO2(g)
slow fast
For the mechanism described in the previous question, which species are intermediates? A
O3 and NO2
B
O and NO
C
NO only
D O only
From the stoichiometric equation, NO and O3 are reactants, while NO2 and O2 are products. From the mechanism, O is an intermediate as it is formed in step 1, and subsequently used up in step 2. 24.
Some standard redox potentials values are given in the table below. Electrode reaction Fe3+(aq) + e− Fe2+(aq) Sn4+(aq) + 2e− Sn2+(aq) Ce4+(aq) + e− Ce3+(aq)
Eo/ V +0.77 +0.15 +1.45
Which of the following reactions would NOT be expected to occur under standard conditions? 9647/01 NYJC Promotional Exam 2010
11 A B C D
Ce4+(aq) + Fe2+(aq) → Ce3+(aq) + Fe3+(aq) Sn2+(aq) + 2Fe3+(aq) → Sn4+(aq) + 2Fe2+(aq) 2Ce4+(aq) + Sn2+(aq) → 2Ce3+(aq) + Sn4+(aq) Sn4+(aq) + 2Fe2+(aq) → Sn2+(aq) + 2Fe3+(aq)
Ecell(A) =+0.68V, Ecell(B) = +0.62V, Ecell(C) = +1.30V > 0. Ecell(D) = -0.62V < 0. Reaction is not feasible. 25.
Electrolysis of aqueous copper(II) sulphate was carried out using copper electrodes and a steady current. Which graph shows the change in mass of the cathode with time?
ANS A ItM mCu = , mCu is proportional to time, t. ZF 26.
Two cells are connected in series as shown in the diagram where M, N, O and P are electrodes.
M
lead
1 mol dm dil HNO3
N
O
P
platinum
-
-
1 mol dm FeCl3 (aq)
Which of the following correctly shows the products formed at each electrode?
A B C D
M O2 O2 Pb2+ Pb2+
N H2 Pb H2 H2
O O2 Cl2 Cl2 O2
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P Fe2+ H2 H2 Fe2+
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12 M Sign + Electrode Anode [O] Species Pb, H2O 2+ θ E values Pb /Pb -0.13 O2/H2O- +1.23 Product Pb2+
N Cathode [R] H+, H2O H+/H2 0.00 H2O/H2 -0.83 H2
O + Anode [O] Cl-, H2O Cl2/Cl- +1.36 O2/H2O +1.23 O2
P Cathode [R] Fe3+, H2O Fe3+/Fe2++0.77 H2O/H2 -0.83 Fe2+
27. A current of 5 amperes was passed for 5 seconds through a molten salt
containing X3+ ions. The mass of X deposited was 5 g. If M is the relative molecular mass of X and e is the charge on an electron, then an expression of Avogadro Constant is given by
5M / 3e 125 / 3Me 3e / 5M 3Me / 125
A B C D +
−
X 3 + 3e → X 5 x5 5 M = 5 3 3 M 5 M
It = nzF ⇒ F =
F = Le ⇒ L = 28.
3e
The diagram shows the structure of vitamin C. OH
HO C
O
C
C
* CH
* CH
CH2
OH
OH O
How many chiral centres are there in one molecule? A
1
B
2
C
3
2 chiral centres indicated above.
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D 4
13 Four isomers of C6H12 are shown below. H3C
H3C
CH3 C
C
C
C
C
H
C2 H5
H
C2 H5
C
H3C
CH3
CH3
C CH3
C CH3
H
3
2
1
H
C2 H5
C2 H 5
4
Which of the following pairs consists of a pair of cis-trans isomers?
29.
A
1 and 2
B
1 and 3
C
1 and 4
D 2 and 4
Note 1 and 3 are the same molecule. 1(or 3) and 2 are cis-trans isomers. 4 is a structural isomer of 1,2,3 as the groups are connected differently. 30.
Vitamin A has the structural formula CH3
CH3 CH
CH
c-t
C
CH3 CH
CH
c-t
CH
c-t
C
CH
c-t
CH2 OH
CH3 CH3
What is the total number of stereoisomers (cis-trans and optical) of this molecule? A
8
B
16
C
32
D 64
There are a total of 4 geometric centres indicated above (note no optical isomers present). Hence a total of 24=16 steroisomers. Note the C=C bond in the ring cannot exhibit geometric isomerism as only the cisform is stable.
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14 Section B For each questions in this section, one or more of the three numbered statements 1 to 3 may be correct. The responses A to D should be selected on the basis of A B C D 1, 2 and 3 are 1 and 2 only are 2 and 3 only are 1 only is correct correct correct correct No other combination of statements can be used as a correct response.
31.
In an experiment, 10 cm3 of an organic compound in the gaseous state were sparked with an excess of oxygen. 20 cm3 of carbon dioxide and 5 cm3 of nitrogen were obtained among the products. All gas volumes were measured at the same temperature and pressure. Which of the following molecular formulae would fit these data? C2H7N C2H3N C2H6N2
1 2 3 ANS B
C x H y N z + ( x + nCO2 nC x H y
=
x
=
1
20 10
y 4
)O2 →
z 2
N 2 + xCO2 +
y 2
H 2O
⇒ x = 2
z n N 2 nC x H y 32.
5 = 2 = ⇒ z = 1 1
10
The compound ammonium chloride, NH4Cl is prepared commercially by reacting NH3 with HCl. Which of the following types of bonding are found in NH4Cl? 1 2 3
Ionic Bonding Covalent Bonding Dative Bonding
ANS A Ionic bonds are present between NH 4+ and Cl-. Within NH4+ cation, there are covalent bonding and dative bonding.
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15 33.
Which of the following pairs has the first species having a stronger bond than the second? 1 2 3
Li and K MgCl2 and LiCl O-H and S-H
ANS A 1. Metallic bonding in Li is stronger than that in K as Li+ has a smaller ionic radius. 2. Ionic bond in MgCl2 is stronger than that LiCl as Mg2+ has a higher charge of +2. (Note: charge factor outweighs radius factor) 3. O-H bond is stronger than S-H bond as O-H bond is polar and there is extra attraction between the opposite partial charges. 34. A real gas deviates from ideal gas behaviour because molecules in a real gas
1 2 3
have different speed. have a definite size. are subjected to intermolecular forces.
ANS C 2 of the Assumptions of ideal gas are: a. The gas particles do not exert any forces of attraction on each other. b. The volume of the gas particles is negligible compared to the volume of the container. Hence 2 & 3 are true. Real gas particles do not move at uniform speed and speed of molecules is not part of ideal gas assumption, therefore 1 is wrong. 35. The radius and charge of six ions are given below.
Ion Radius/ nm
J+ 0.14
L+ 0.18
M2+ 0.15
X0.14
Y0.18
Z20.15
The ionic solids MZ, JX and LY are of the same lattice type. Which of the following statements are correct?
1 2 3
The melting point of JX is higher than that of LY. The numerical value of the lattice energy of MZ is greater than that of JX. The numerical value of the hydration energy of J + is smaller than that of M2+.
ANS A Lattice energy/ melting point is proportional to IZ+ Z-I/(r + + r -) So for JX it is α 1 x 1/(0.14 + 0.14) = 51.02 So for LY it is α 1 x 1/(0.18 + 0.18) = 30.80 So for MZ it is α 2 x 2/(0.15 + 0.15) = 177.7
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16 Hydration energy is proportional to charge /radius of relevant ion For J+ it is α 1/0.14 = 7.14 For M2+ it is α 2/0.15 = 13.3 Note : It is not necessary to do the above calculations. Answers can be derived from estimations
36.
Methanol is manufactured industrially by the catalytic reaction shown. CO (g) + 2H2 (g) CH3OH (g) ; ΔH = -92 kJ mol-1 The operating conditions are: 250 o C ; a pressure between 50 atm and 100 atm ; a copper-based catalyst. Which factor influences the choice of these conditions? 1 At lower temperature, the rate of formation of the product CH3OH decreases. 2 At lower pressure, the rate of formation of the product, CH3OH increases. 3 The catalyst increased the equilibrium yield of the product, CH3OH.
ANS D Equilibrium yield is increased by low temperature and high pressure. However, temperature cannot be too low as it affect rate of formation, hence 1 is correct. Low pressure does not increase rate of formation and catalyst only increase rate but not equilibrium yield. Therefore 2 & 3 are wrong. 37.
Which of the following statements are correct about the effect of a homogeneous catalyst for a reversible reaction? 1 2 3
It is usually involved in the rate determining step. It increases the forward and backward rate constants. It increases the equilibrium constant.
ANS B 1. A homogenous catalyst reacts via the intermediate compound theory, where it usually involved in the rate-determining step of the mechanism so as to lower the activation energy of the reaction. 2. A homogenous catalyst lowers the activation energy of the reaction, and for a reversible reaction, it increases the both the forward and backward rate constants. 3. The equilibrium constant is unaffected by a catalyst. It is only affected by temperature. 38.
What are the conditions usually quoted for the standard electrode potential of hydrogen to be 0.00 V? 1 2 3
The concentration of H+ (aq) is 1 mol dm-3 The atmospheric pressure is exactly 1 atm The temperature is 0 oC
ANS D Standard Conditions: [Ion] = 1 mol dm-3, Partial pressure of gas = 1 atm, Temperature = 298K. 9647/01 NYJC Promotional Exam 2010
17 39. A
cell involving aqueous manganate(VII) is shown.
potassium
iodide
and
acidified
potassium
V
Pt
salt bridge
−3
0.10 mol dm potassium iodide, 25 oC
Pt 0.10 mol dm−3 potassium manganate(VII) containing sulfuric acid, 25 oC
Which observations about this arrangement are correct?
1 2 3
The voltmeter shows a reading of about 0.98 V. The potassium iodide solution turns brown. The purple colour of the potassium manganate(VII) solution becomes less intense.
ANS A Eθ(I2/I-) = +0.54 V [O], Eθ(MnO4-/Mn2+) = +1.52 V [R] ⇒ Eθcell = +0.98V. I- is oxidized to I2 (brown) and MnO4- (deep purple) is reduced to Mn2+ (pale pink) 40.
2-Methylbuta-1,3-diene can be polymerised to make synthetic rubbers. The structure of this monomer is shown below.
CH3 H2C
C
CH
CH2
Which of the following statements about 2-methylbuta-1,3-diene are correct? 1 2 3
It has 12 sigma bonds in total. It is NOT optically active. Four of its carbon atoms are sp2 hybridised.
ANS A 1. Draw the full displayed formula to count the sigma bonds. 2. It is not optically active as there is no chiral carbon present hence no optical isomers. 3. The 4 C in the C=C are sp2 hybridized.
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