To which family does $Ricinus$ $communis$ belong?

If in a $\triangle ABC$,$\frac{1}{a+c} + \frac{1}{b+c} = \frac{3}{a+b+c}$,then $\angle C$ is equal to (in $^{\circ}$)

Which of the following pairs of $2,3$-butanediol are enantiomeric?

The bleaching action of $SO_2$ is due to its .........

In which of the following reactions is the product an ether?

Four smooth steel balls of equal mass at rest are free to move along a straight line without friction. The first ball is given a velocity of $0.4 \, m/s$. It collides head-on with the second elastically,the second one similarly with the third,and so on. The velocity of the last ball is .......... $m/s$.