If ${}^n{P_4} : {}^n{P_5} = 1 : 2$,then $n = $

There is a uniform electric field of strength $10^3 \ Vm^{-1}$ 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 $10 \ ms^{-1}$. Its speed in $ms^{-1}$ after $10 \ s$ is (Neglect gravitation).

Match List-$I$ with List-$II$ for the composition of substances and select the correct answer using the code given below the lists.

List-$I$ (Substances)	List-$II$ (Composition)
$A$. Plaster of Paris	$i$. $CaSO_4 \cdot 1/2H_2O$
$B$. Epsomite	$ii$. $MgSO_4 \cdot 7H_2O$
$C$. Kieserite	$iii$. $MgSO_4 \cdot H_2O$
$D$. Gypsum	$iv$. $CaSO_4 \cdot 2H_2O$
	$v$. $CaSO_4$

In an experiment of a simple pendulum, the errors in the measurement of length of the pendulum $(L)$ and time period $(T)$ are $3 \%$ and $2 \%$, respectively. The maximum percentage error in the value of $\frac{L}{T^2}$ is (in $\%$)

The coefficient of $x^k$ in the expansion of $\frac{1-2x-x^2}{e^{-x}}$ is

Which one of the following oxides is expected to exhibit paramagnetic behaviour?