A thin horizontal circular disc is rotating about a vertical axis passing through its centre. An insect is at rest at a point near the rim of disc. The insect now moves along a diameter of the disc to reach its other end. During the journey of the insect, the angular speed of the disc

Assertion The angular momentum of system always remain constant.

Reason For a system, $$\tau_{\mathrm{ext}}=\frac{d L}{d t}=0$$