Give reasons for the following:
$A$. Covalent bonds are directional bonds while ionic bonds are non-directional.
$B$. Water molecule has bent structure whereas carbon dioxide molecule is linear.
$C$. Ethyne molecule is linear.

(N/A) . $A$ covalent bond is formed by the overlapping of atomic orbitals. The direction of overlapping gives the direction of the bond. In an ionic bond,the electrostatic field of an ion is non-directional.
Each positive ion is surrounded by a number of anions in any direction depending upon its size and vice-versa. That is why covalent bonds are directional and ionic bonds are non-directional.
$B$. In $H_{2}O$,the oxygen atom is $sp^{3}$ hybridised with two lone pairs. The four $sp^{3}$ hybridised orbitals possess a tetrahedral geometry with two corners occupied by hydrogen atoms and the other two by the lone pairs.
The bond angle is reduced to $104.5^{\circ}$ from $109.5^{\circ}$ because of greater repulsive forces between $lp-lp$ (lone pair-lone pair) and the molecule gains a $V$-shape or bent structure (angular structure).
In the $CO_{2}$ molecule,the carbon atom is $sp$-hybridised. The two $sp$ hybrid orbitals are oriented in opposite directions forming an angle of $180^{\circ}$.
$O=C=O$
So,the $H_{2}O$ molecule has a bent structure and the $CO_{2}$ molecule is linear.
$C$. In the ethyne molecule,both carbon atoms are $sp$ hybridised,having two unhybridised orbitals,i.e.,$2p_{x}$ and $2p_{y}$. The two $sp$ hybrid orbitals of both carbon atoms are oriented in opposite directions forming an angle of $180^{\circ}$.
So,the ethyne molecule is linear.