If the maximum velocity with which an electron can be emitted from a photocell is $4 \times 10^8 \,cm/sec$,the stopping potential is ............ $V$ (mass of electron $= 9 \times 10^{-31} \,kg$).

Which pair of the following belongs to Basidiomycetes?

$A$ student is to answer $10$ out of $13$ questions in an examination such that he must choose at least $4$ from the first $5$ questions. The number of choices available to him is

If $A$ and $B$ are events of a random experiment such that $P(A \cup B) = \frac{4}{5}$,$P(\bar{A} \cup \bar{B}) = \frac{7}{10}$ and $P(B) = \frac{2}{5}$,then $P(A)$ equals

$A$ sonometer wire is stretched by hanging a metal bob. The fundamental frequency of vibration of the wire is '$n_1$'. When the bob is completely immersed in water,the frequency of vibration of the wire becomes '$n_2$'. The relative density of the metal of the bob is

Which of the following structures corresponds to the product expected when an excess of $C_6H_6$ reacts with $CH_2Cl_2$ in the presence of anhydrous $AlCl_3$?