The first,second and third Ionisation energies ($E_1, E_2$ and $E_3$) for an element are $7 \ eV, 12.5 \ eV$ and $42.5 \ eV$ respectively. The most stable oxidation state of the element will be

The base current in a transistor circuit changes from $45 \mu A$ to $140 \mu A$. Accordingly,the collector current changes from $0.2 \text{ mA}$ to $4.0 \text{ mA}$. The current gain is

The electric current $i$ in the circuit shown is (in $A$)

Let $z = a - \frac{i}{2}$,where $a \in R$. Then $|i + z|^2 - |i - z|^2$ is equal to

$A$ codon has a sequence of $\underline{A}$,and specifies a particular $\underline{B}$ that is to be incorporated into a $\underline{C}$. What are $\underline{A}, \underline{B}, \underline{C}$ ?
$\underline{A} \quad \underline{B} \quad \underline{C}$

In which of the following reactions is benzaldehyde formed from benzoyl chloride and hydrogen in the presence of $Pd/BaSO_4$?