Explanation

(a)
Angle strain in cyclopropane is $24{^\circ}44'$
$\theta = \left\lbrack 180 - \frac{360}{n} \right\rbrack$
$= \left\lbrack 180 - \frac{360}{3} \right\rbrack$
$= 180 - 120 = 60{^\circ}$
Angle strain $\alpha = \frac{1}{2}\left\lbrack 109{^\circ}28^{'} - \theta \right\rbrack$
$= \frac{1}{2}\left\lbrack 109{^\circ}28^{'} - 60{^\circ} \right\rbrack$
$= 24{^\circ}44'$