The most important ore of tin is:

Which of the following compounds is an optically inactive compound?

$A$ simple pendulum has a periodic time $T_1$ when it is on the surface of the Earth of radius $R$. Its periodic time is $T_2$ when it is taken to a height $R$ above the Earth's surface. The value of $\frac{T_2}{T_1}$ is

If $(-2, 6)$ is the image of the point $(4, 2)$ with respect to the line $L = 0$,then $L$ is equal to

Cuscuta is an example of

The synthesis of crotonaldehyde from acetaldehyde is an example of $.......$ reaction.