(i) If both the angles are acute then two angles can’t be supplementary because:

Acute angle is always less than 90^o and addition of any two angles less than 90^o can never be equal to 180^o

Hence,

Two acute angles cannot be in a supplementary angle pair

(ii) If both the angles are obtuse then two angles can’t be supplementary because:

Obtuse angle is always greater than 90^o and addition of any two angles greater than 90^o can never be equal to 180^o

Hence,

Two obtuse angles cannot be in a supplementary angle pair

(iii) if both the angles are right angles then the pair of angles must be supplementary because:

Right angle is equal to 90^o and addition of two right angles is equal to 180^o

i.e., 90^o + 90^o = 180^o

Hence,

Two right angles form a supplement angle of pair