How many sigma and pi bonds are present in ${\mathrm{C}}_2{\mathrm{H}}_4$?

Is there any change in the hybridisation of boron and nitrogen atoms as a result of the following reaction?

${\mathrm{BF}}_3+{\mathrm{NH}}_3\stackrel{ }{\to }{\mathrm{F}}_3{\mathrm{BNH}}_3$

Use Lewis symbols to show electron transfer between the following pairs of atoms to form cations and anions.

$\mathrm{K}$ and $\mathrm{S}$.

Use Lewis symbols to show electron transfer between the following pairs of atoms to form cations and anions.

$\mathrm{Ca}$ and $\mathrm{O}$.