Let $PQR$ be a right-angled isosceles triangle,with the right angle at $P(2, 1)$. If the equation of the line $QR$ is $2x + y = 3$,then the equation representing the pair of lines $PQ$ and $PR$ is:

Biolistics (gene gun) is suitable for

$0.066 \ g$ of metal was deposited when a current of $2 \ A$ is passed through a metal ion solution for $100 \ s$. What is the electrochemical equivalent (in $g \ C^{-1}$) of the metal?

If $\int \sec ^2 x \operatorname{cosec}^4 x \, dx = -\frac{1}{3} \cot ^3 x + k \tan x - 2 \cot x + C$,then $k$ is equal to

Given below are $2$ statements:
Statement $I$: The number of species among $BF_4^-$,$SiF_4$,$XeF_4$ and $SF_4$,that have unequal $E-F$ bond lengths is $2$. Here,$E$ is the central atom.
Statement $II$: Among $O_2^-$,$O_2^{2-}$,$F_2$ and $O_2^+$,$O_2^-$ has the highest bond order.
In the light of the above statements,choose the correct answer from the options given below

Along the $X$-axis,three charges $\frac{q}{2}, -q$ and $\frac{q}{2}$ are placed at $x=0, x=a$ and $x=2a$ respectively. The resultant electric potential at $x=a+r$ (if $a \ll r$) is: ($\varepsilon_0$ is the permittivity of free space)