Which of the following haloalkanes will undergo $S_{N}2$ reaction at the fastest rate?

The same current is flowing in two alternating circuits. The first circuit contains only an inductor and the second contains only a capacitor. If the frequency of the $e.m.f.$ of the $ac$ source is increased,what will be the effect on the value of the current in these circuits?

Pure $Si$ at $500\, K$ has equal number of electron $(n_e)$ and hole $(n_h)$ concentrations of $1.5 \times 10^{16} \,m^{-3}$. Doping by indium increases $n_h$ to $4.5 \times 10^{22} \,m^{-3}$. The doped semiconductor is of

One litre of an aqueous solution contains $0.15 \ mol$ of $CH_3COOH$ $(pK_a = 4.8)$ and $0.15 \ mol$ of $CH_3COONa$. After the addition of $0.05 \ mol$ of solid $NaOH$ to this solution,the $pH$ will be

Water rises to a height $h$ in a capillary tube. If the length of the capillary tube above the surface of water is made less than $h$,then

Two photons of energy $2.5 \ eV$ and $3.5 \ eV$ fall on a metal surface of work function $1.5 \ eV$. The ratio of the maximum velocities of the photoelectrons emitted from the metal surface is