**Question:**

In Fig. 16.19, *ABCD* is a quadrilateral.

(i) Name a pair of adjacent sides.

(ii) Name a pair of opposite sides.

(iii) How many pairs of adjacent sides are there?

(iv) How many pairs of opposite sides are there?

(v) Name a pair of adjacent angles.

(vi) Name a pair of opposite angles.

(vii) How many pairs of adjacent angles are there?

(viii) How many pairs of opposite angles are there?

**Solution:**

(i) $(\mathrm{AB}, \mathrm{BC})$ or $(\mathrm{BC}, \mathrm{CD})$ or $(\mathrm{CD}, \mathrm{DA})$ or $(\mathrm{AD}, \mathrm{AB})$

(ii) $(\mathrm{AB}, \mathrm{CD})$ or $(\mathrm{BC}, \mathrm{DA})$

(iii) Four

(iv) Two

(v) $(\angle \mathrm{A}, \angle \mathrm{B})$ or $(\angle \mathrm{B}, \angle \mathrm{C})$ or $(\angle \mathrm{C}, \angle \mathrm{D})$ or $(\angle \mathrm{D}, \angle \mathrm{A})$

(vi) $(\angle \mathrm{A}, \angle \mathrm{C})$ or $(\angle \mathrm{B}, \angle \mathrm{D})$

(vii) Four

(viii) Two