सही विकल्प है (B) 140°
हम जानते हैं कि त्रिज्या स्पर्शरेखा पर लंबवत होती है।
\(\therefore \angle OML = 90^\circ\)
\(\Rightarrow \angle O M N+\angle N M L =90^{\circ}\)
\(\Rightarrow \angle O M N+70^{\circ} =90^{\circ}\)
\(\Rightarrow \angle O N N =90^{\circ}-70^{\circ}\)
\(\Rightarrow \angle O M N =20^{\circ}\)
\(O M=O N\quad[\text {Radii of a Circle] }\)
\(\angle OMN=\angle O N M=20^{\circ} \quad \text{[Base angles of equal sides are also equal]}\)
\(\triangle MON\) में,
\(\angle O M N+\angle M O N+\angle O N M=180^{\circ} \quad \mathrm{[\because Sum\ of \ angles\ of\ a\ triangle\ is\ 180^\circ]}\)
\(20^{\circ}+\angle M O N+20^{\circ} =180^{\circ}\)
\(\angle M O N+40^{\circ} =180^{\circ} \)
\(\angle M O N =180^{\circ}-40^{\circ} \)
\(\therefore \angle M O N =140^{\circ}\)
