The number of elements present in the fourth period is

In the circuit shown here,$E_1 = E_2 = E_3 = 2 \, V$ and $R_1 = R_2 = 4 \, \Omega$. The current flowing between points $A$ and $B$ through battery $E_2$ is

The sum of all the solution $(s)$ of the equation $\sin^{-1} 2x = \cos^{-1} x$ is

If $X$ is a Poisson variate such that $P(X=1)=P(X=2)$, then $P(X=4)$ is equal to

At higher altitude,the boiling point of water is $95\, ^oC$. The amount of $NaCl$ added to $1\, kg$ of water $(K_b = 0.52\, K\, kg\, mol^{-1})$ in order to raise the boiling point of the solution to $100\, ^oC$ (assuming $90\%$ ionization of $NaCl$) is .......... $g$.

$A$ person speaking normally produces a sound intensity level of $40\, dB$ at a distance of $1\, m$. If the threshold intensity level for reasonable audibility is $20\, dB$,the maximum distance at which he can be heard clearly is ..... $m$.