In which plants does pollination occur exclusively by wind?

$A$ ray of light refracts from medium $1$ into a thin layer of medium $2$,crosses the layer,and is incident at the critical angle on the interface between medium $2$ and $3$ as shown in the figure. If the angle of incidence of the ray is $\theta$,the value of $\theta$ is

Pure hydrogen sulphide is stored in a tank of $100 \ L$ capacity at $20 \ ^oC$ and $2 \ atm$ pressure. The mass of the gas will be ................. $g$.

$A$ bag contains $n$ white and $n$ black balls. Pairs of balls are drawn at random without replacement successively,until the bag is empty. If the number of ways in which each pair consists of one white and one black ball is $14400$,then $n$ is equal to

The body of the ovule is fused with the funicle at:

$Ni$ anode is used in the electrolytic extraction of