Assertion and Reason Type Question

The strength of the metallic bond depends on the number of valence electrons and the charge of the nucleus.

For Potassium, the atomic number Z=19

The electronic configuration of potassium is given as below

$\mathrm{E}.\mathrm{C} \mathrm{of} \mathrm{K}\to 1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^1$

There is one valence electron in potassium (K).

For Gold, the atomic number Z=79

The electronic configuration of Gold is given as below

$\mathrm{E}.\mathrm{C} \mathrm{of} \mathrm{Au}\to \left[\mathrm{Xe}\right]4{\mathrm{f}}^{14}5{\mathrm{d}}^{10}6{\mathrm{s}}^1$

Gold has one valence electron in the ground state but it is a transition element it shows more than one valence by loss of electrons.  Therefore, Gold (Au) has more number of valence electrons and greater charge of the nucleus than potassium (K).  Hence both assertion and reason are correct and reason correctly explains of assertion