A disc is rotating about its own axis with angular frequency 100 rpm. When a mass of 100 g is placed at l0 cm from its centre then its angular frequency becomes 50 rpm. The moment of inertia of the disc is :

• A

  5 x 10⁴ gcm²

• B

  10⁴ gcm²

• C

  10³ gcm²

• D

  10⁵ gcm²