The mean and the standard deviation (s.d.) of $10$ observations are $20$ and $2$ respectively. Each of these $10$ observations is multiplied by $p$ and then reduced by $q$,where $p \neq 0$ and $q \neq 0$. If the new mean and new s.d. become half of their original values,then $q$ is equal to

The number of unpaired electrons in $Zn^{2+}$ is

If $S_n = 1^3 + 2^3 + \ldots + n^3$ and $T_n = 1 + 2 + \ldots + n$,then

If $m$ and $\sigma ^2$ are the mean and variance of random variable $X$,whose distribution is given by:

$X=x$	$0$	$1$	$2$	$3$	$4$
$P(X=x)$	$\frac{1}{3}$	$\frac{1}{2}$	$0$	$\frac{1}{6}$	$0$

then:

There is a uniform electric field of strength $10^3 \, V/m$ along the $y$-axis. $A$ body of mass $1 \, g$ and charge $10^{-6} \, C$ is projected into the field from the origin along the positive $x$-axis with a velocity of $10 \, m/s$. Its speed in $m/s$ after $10 \, s$ is (Neglect gravitation).

$A$ monoatomic ideal gas,initially at temperature $T_1$,is enclosed in a cylinder fitted with a frictionless piston. The gas is allowed to expand adiabatically to a temperature $T_2$ by releasing the piston suddenly. If $L_1$ and $L_2$ are the lengths of the gas column before and after expansion respectively,then $\frac{T_1}{T_2}$ is given by: