In a series of $2n$ observations,half of the observations are equal to $a$ and the remaining are equal to $-a$. If the standard deviation of the observations is $2$,then what is the value of $|a|$?

Regarding the molecular orbital $(MO)$ energy levels for homonuclear diatomic molecules, the $\text{INCORRECT}$ statement$(s)$ is$($are$)$
$(A)$ Bond order of $Ne _2$ is zero.
$(B)$ The highest occupied molecular orbital $\text{(HOMO)}$ of $F_2$ is $\sigma$-type.
$(C)$ Bond energy of $O _2^{+}$is smaller than the bond energy of $O _2$.
$(D)$ Bond length of $Li _2$ is larger than the bond length of $B _2$

The shortest distance between the lines $\frac{x - 3}{3} = \frac{y - 8}{-1} = \frac{z - 3}{1}$ and $\frac{x + 3}{-3} = \frac{y + 7}{2} = \frac{z - 6}{4}$ is:

Names of units of some physical quantities are given in List-$I$ and their dimensional formulae are given in List-$II$. Match the correct pairs in the lists:

$A$. $Pa \cdot s$	$(i)$ $[L^2 \ T^{-2} \ K^{-1}]$
$B$. $N \cdot m \cdot K^{-1}$	$(ii)$ $[M \ L \ T^{-3} \ K^{-1}]$
$C$. $J \cdot kg^{-1} \cdot K^{-1}$	$(iii)$ $[M \ L^{-1} \ T^{-1}]$
$D$. $W \cdot m^{-1} \cdot K^{-1}$	$(iv)$ $[M \ L^2 \ T^{-2} \ K^{-1}]$

Which of the following is $NOT$ a characteristic of the phylum $Annelida$?

If $z=\log (\tan x+\tan y)$, then $(\sin 2x) \frac{\partial z}{\partial x}+(\sin 2y) \frac{\partial z}{\partial y}$ is equal to