91Ó°ÊÓ

Each of the given compounds is written in its structural form. The hydrogen atoms or lone pair of electrons are placed wherever required to satisfy valency.

The number of surrounding atoms and groups are counted around each atom.

a. The central carbon atom has four atoms around it in a tetrahedral geometry. Therefore, the bond angles in between each of the bonded atoms attached to this carbon are$109.5°$.

Structure of (a)

b. Both nitrogen and oxygen atoms have four groups (including the lone pairs) around them. Hence, the bond angles are $109.5°$.

Structure of (b)

c. The carbon and the nitrogen atom in the $-\mathrm{C}=\mathrm{N}-$ bond have three groups around them. So, the bond angles are $120°$. The carbon in the $-{\mathrm{CH}}_3$has four groups around it. Hence, the bond angle that this carbon makes is $109.5°$

Structure of (c)

d. Both the carbon atoms in the $-\mathrm{C}≡\mathrm{C}-$bond have two groups around them. Hence, the angle between the groups around them is $180°$.

The other two carbon and oxygen atoms have four groups around them, including the lone pairs of electrons. Hence, their bond angles are $109.5°$.

Structure of (d)

e. All the carbon atoms have three groups around them. Hence, the bond angles are $120°$.

Structure of (e)