Which of the following metals releases hydrogen gas upon reaction with cold dilute $HNO_3$?

If the pair of lines given by $(x^2+y^2) \cos^2 \theta = (x \cos \theta + y \sin \theta)^2$ are perpendicular to each other,then $\theta$ is equal to

An electrochemical cell is fueled by the combustion of butane at $1$ bar and $298 K$ . Its cell potential is $\frac{ X }{ F } \times 10^3$ volts, where $F$ is the Faraday constant. The value of $X$ is $...$ .
Use : Standard Gibbs energies of formation at $298 K$ are : $\Delta_f G_{ CO _2}^{ o }=-394 kJ mol ^{-1}; \Delta_f G_{\text {water }}^{ o }=-237 kJ mol ^{-1} ; \Delta_f G_{\text {butane }}^{ o }=-18 kJ mol ^{-1}$

Water is pumped from a depth of $10\, m$ and delivered through a pipe of cross section $10^{-2}\, m^2$. If it is needed to deliver a volume of $10^{-1}\, m^3$ per second,the power required will be: ............ $kW$

The graph which represents the variation of mean kinetic energy of molecules with temperature $t^{\circ}C$ is

Identify $A$ and $B$ in the following reaction:
$C_2H_5Cl \xrightarrow{A} C_2H_5OH \xleftarrow{B} C_2H_5Cl$