Organic chemistry pyqs

 10 basic questions in Organic Chemistry for Scientific assistant (PYQS)

1. How many electrons occupy bonding molecular orbitals of CN triple bond?

1. 2
2. 4
3. 6
4. 8

Answer: 6 electrons

Explanation: CN has a triple bond which means it has one sigma bond and one pi bond. One sigma bond contains two electrons and one pi bond contains 4 electrons which means CN triple bond contains a total of 6 bonding electrons

2. Which of the following compounds is most acidic?

1. CH3CH2OH
2. CH3COOH
3. CH3NH2
4. CH3Cl

Answer: CH3COOH

Explanation: CH3CH2OH is very weak acid its conjugate base is not resonance stabilized

                      CH3COOH is acidic and its conjugate base is resonance stabilized

                      CH3NH2 is a base

                      CH3Cl is neutral not acidic

3. Which of the following is an example of  Aromatic nucleophilic substitution reactions?

1. Friedel crafts alkylation
2. Friedel crafts acylation
3. Sandmeyer reaction
4. Williamson ether synthesis

Answer: Sandmeyer reaction

Explanation: Friedel crafts alkylation and acylation is an aromatic electrophilic substitution reaction and Williamson ether synthesis is nucleophilic substitution reaction but not aromatic. Sandmeyer reaction involves replacement of N2 by Nucleophile or cyanide using Cu(I) as catalyst.

 

4. Which of the following will act as buffer?

1. CH3COOH/CH3COONa
2. CH3COONH4
3. Nacl
4. NH4OH/NH4Cl mixture

Answer: Option 1 and 4

Explanation: A buffer is a solution that resists pH change

                      It is formed by a weak acid and its conjugate base or a weak base and its conjugate acid

                      In CH3COOH/CHCOONa it a weak acid and its conjugate base and in NH4OH/NH4Cl                          mixture it is weak base and its conjugate acid.

5. Which of the following is an example of metamerism?

1. CH3CH2OCH3 and CH3-O-CH2-CH2-CH3
2. CH3-C=O-CH3 and CH3-CH2-CHO
3. CH3-CH2-CH2-OH and CH3-CHOH-CH3
4. None of the above

Answer: Option 1

Explanation: Isomers having same functional group, same molecular formula but different alkyl groups attached to functional groups is called Metamerism. In Option 1 the -O- group is attached to ethyl in the first molecule and propyl in the second molecule

6. Composition of Ziegler Natta Catalyst is

1. (Et3)3Al.TiCl2
2. (Me)3Al.TiCl2
3. (Et)3Al.TiCl4
4. (Et)3Al.PtCl4

Answer: (Et)3Al.TiCl4

Explanation: Ziegler Natta catalyst is used in the polymerization of alkenes to produce polymers with specific arrangements of side groups. It convert Polyethylene to Linear High Density Polyethylene(LDPE)

7. Order of boiling point of isomeric primary, secondary, and tertiary amines is 

1. Secondary>Primary>tertiary
2. Primary>Secondary>Tertiary
3. Tertiary>Primary>Secondary
4. Secondary>Tertiary>Primary

Answer: Primary>Secondary>Tertiary

Explanation: Strong hydrogen bonds leads to higher boiling point. In primary amines there is two hydrogen groups forming maximum hydrogen bonds.

8. Which of the following bonds is most polar?

1. C-H
2. O-H
3. C-O
4. N-H

Answer: O-H

Explanation: Based on Pauling's electronegativity scale, the more the electronegativity difference the more the bond polarity

9. Which of the following elements is less electronegative than Carbon?

1. F
2. N
3. Cl
4. Si

Answer:  Si

Explantion: Based on Pauling's electronegativity scale

10. Which of the following is not an allotrope of  Carbon?

1. Graphite
2. Diamond
3. Silica
4. Fullerene

Answer: Silica

Explanation: Silica (SiO2) is a compound made of Silicon and Oxygen not Carbon

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