Which of the following gases present in the air darkens the surface painted with white lead?

If the rate of disappearance of $N_2O_5$ in the following reaction is $1.2 \times 10^{-5} \ mol \ L^{-1} \ s^{-1}$,the rate of production of $NO_2$ in $mol \ L^{-1} \ s^{-1}$ is:
$2 \ N_2O_{5(g)} \longrightarrow 4 \ NO_{2(g)} + O_{2(g)}$

The depletion layer in the $p-n$ junction is caused by

Which of the following is an azo dye?

$A$ parallel plate capacitor with air as medium between the plates has a capacitance of $10\,\mu F$. The area of the capacitor is divided into two equal halves and filled with two media as shown in the figure having dielectric constants $k_1 = 2$ and $k_2 = 4$. The capacitance of the system will now be.......$\mu F$.

The correct stability order for the following carbocations is: