Which of the following have $3C-2e^-$ bond?
$I.$ $Al_2Cl_6$
$II.$ $B_2H_6$
$III.$ $Fe_2Cl_6$
$IV.$ $Si_2H_6$

An electron moves with speed $2 \times 10^5 \ m/s$ along the positive $x$-direction in the presence of a magnetic induction $\vec{B} = \hat{i} + 4\hat{j} - 3\hat{k}$ (in $Tesla$). The magnitude of the force experienced by the electron in Newtons is (charge on the electron = $1.6 \times 10^{-19} \ C$).

The de-Broglie wavelength of a particle accelerated with $150 \ V$ potential is $10^{-10} \ m$. If it is accelerated by $600 \ V$ potential difference,its wavelength will be ........... $\mathring{A}$.

Which of the following substances is used in the laboratory to dry natural gas quickly?

Which of the following is the strongest acid?

The mean of four observations is $3$. If the sum of the squares of these observations is $48$,then their standard deviation is