(i) 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’s why covalent bonds are directional bonds while ionic bonds are non-directional.

(ii) In a water molecule, the oxygen atom is sp³ hybridized and has two lone pairs of electrons.

The shape acquired by 4 molecular orbital is tetrahedral geometry with two hydrogen atoms occupying the corner and the other two orbitals by lone pair of electrons.

The bond angle is reduced to 104.5° from 109.5° due to greater repulsive forces between lone pairs. Thus, a molecule thus acquires a V-shape or bent structure (angular structure).

In carbon dioxide molecules, the carbon molecule is sp hybridized.

The two sp orbitals are oriented in opposite direction to each other. Thus, the shape is linear.

(iii) In the ethyne molecule, both the carbon atoms are sp hybridized. The two sp hybrid orbitals of both the carbon atoms are oriented in the opposite direction forming an angle of 180°.

Thus, the molecule is linear in shape.