Which of the following alkali metal ions has the lowest ionic mobility in an aqueous solution?

The lustre of a metal is due to

Explain the significance of sodium,potassium,magnesium,and calcium in biological fluids.

The correct order of hydration enthalpies is
$A. K^{+}$; $B. Rb^{+}$; $C. Mg^{2+}$; $D. Cs^{+}$; $E. Ca^{2+}$
Choose the correct answer from the options given below:

$A$ metal $(A)$ on heating in nitrogen gas gives compound $(B)$. $(B)$ on treatment with $H_{2}O$ gives a colourless gas which when passed through $CuSO_{4}$ solution gives a dark blue-violet coloured solution. $(A)$ and $(B)$ respectively,are

Which element from the following has the highest negative standard reduction potential?