The total number of $\sigma$ and $\pi$-bonds in pyrophosphoric acid are respectively

Which gases are released when aluminum reacts with concentrated $HCl$ and concentrated $NaOH$ respectively?

If a gas contains only three molecules that move with velocities of $100, 200, 500 \ ms^{-1}$. What is the $rms$ velocity of that gas in $ms^{-1}$?

$ ( X ) + K_2CO_3 + Air \xrightarrow{heat} ( Y ) $
$ ( Y ) + Cl_2 \longrightarrow ( Z ) $ Pink
Which of the following is correct ?

The correct order of ionic radii of $Ce, La, Pm$ and $Yb$ in $+3$ oxidation state is

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