Which one of the following gases can deplete the ozone layer in the upper atmosphere?

The dependence of disturbances due to two waves on time is shown in the figure. The ratio of their intensities $I_1 / I_2$ will be

If $(2,-1,3)$ is the foot of the perpendicular drawn from the origin to the plane, then the equation of the plane is

$A$ tuning fork vibrating with a sonometer having $20 \, cm$ wire produces $5$ beats per sec. The beat frequency does not change if the length of the wire is changed to $21 \, cm$. The frequency of the tuning fork must be ..... $Hz$.

The absolute configurations of the two chiral centers in the following molecule are:

$A$ child is standing at one end of a long trolley moving with a speed $v$ on a smooth horizontal floor. If the child starts running towards the other end of the trolley with a speed $u$,the centre of mass of the system (trolley + child) will move with a speed: