Which of the following is used in the industrial production of nitric acid by the Ostwald process?

$A$ large tank is filled with water to a height $H$. $A$ small hole is made at the base of the tank. It takes $T_1$ time to decrease the height of water to $H/\eta$ (where $\eta > 1$); and it takes $T_2$ time to drain the rest of the water. If $T_1 = T_2$,then the value of $\eta$ is:

If $\alpha$ is a non-real root of the equation $x^6-1=0$,then $\frac{\alpha^2+\alpha^3+\alpha^4+\alpha^5}{\alpha+1}$ is equal to

$A$ disc has mass $m$ and radius $R$. How much tangential force should be applied to the rim of the disc so as to rotate it with angular velocity $\omega$ in time $t$?

If $\int \sin ^{-1}\left(\frac{2 x}{1+x^2}\right) d x=f(x)-\log \left(1+x^2\right)$ then $f(x)$ is equal to

The potential difference $V$ and the current $i$ flowing through an instrument in an $ac$ circuit of frequency $f$ are given by $V = 5 \cos \omega t \text{ volts}$ and $i = 2 \sin \omega t \text{ amperes}$ (where $\omega = 2\pi f$). The power dissipated in the instrument is....$W$