Antihistamines and steroids are administered for which of the following?

During the change of $O_2$ to $O_2^-$ ion,the electron adds to which one of the following orbitals?

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

In which of the following reactions does the hybridisation of the central atom change from $sp^2$ to $sp^3$?

$A$ reversible engine converts one-sixth of the heat supplied into work. When the temperature of the sink is reduced by $62^{\circ} C$,the efficiency of the engine is doubled. The temperatures of the source and sink are

In a transistor circuit,when the base current is increased by $50 \mu A$ keeping the collector voltage fixed at $2 \ V$,the collector current increases by $1 \ mA$. The current gain of the transistor is