Which of the following metals is present in Vitamin $B_{12}$?

$A$ solution of sodium sulphate contains $92 \ g$ of $Na^{+}$ ions per kilogram of water. The molality of $Na^{+}$ ions in that solution in $mol \ kg^{-1}$ is:

The mean and the standard deviation (s.d.) of $10$ observations are $20$ and $2$ respectively. Each of these $10$ observations is multiplied by $p$ and then reduced by $q$,where $p \neq 0$ and $q \neq 0$. If the new mean and new s.d. become half of their original values,then $q$ is equal to

At a certain place,a magnet makes $30$ oscillations per minute. At another place where the magnetic field is double,its time period will be:

The component of vector $\vec{A} = 2\hat{i} + 3\hat{j}$ along the vector $\vec{B} = \hat{i} + \hat{j}$ is:

$A$ mixture of $2$ moles of helium gas (atomic mass = $4 \ amu$) and $1$ mole of argon gas (atomic mass = $40 \ amu$) is kept at $300 \ K$ in a container. The ratio of the rms speeds $\left( \frac{V_{rms}(\text{helium})}{V_{rms}(\text{argon})} \right)$ is