What is the valency of:

Fluorine in ${\mathrm{CaF}}_2$.

What is the valency of:

sulphur in ${\mathrm{SF}}_6$.

What is the valency of:

phosphorus in ${\mathrm{PH}}_3$

What is the valency of:

carbon in ${\mathrm{CH}}_4$

What is the valency of nitrogen in the following compound:

${\mathrm{N}}_2{\mathrm{O}}_3$

What is the valency of nitrogen in the following compound:

${\mathrm{N}}_2{\mathrm{O}}_5$

What is the valency of nitrogen in the following compound:

${\mathrm{NO}}_2$

What is the valency of nitrogen in the following compound:

$\mathrm{NO}$