Identify the type of chemical reaction.

$Mg\left(s\right)+C{l}_2\left(g\right)\to MgC{l}_2\left(s\right)$

The correct option is B Combination reaction
Magnesium ($Mg$) combines with chlorine ($C{l}_2$) to form a new product as magnesium chloride ($MgC{l}_2$). Therfore its a combination reaction and the balanced equation can be written as:
$Mg\left(s\right)+C{l}_2\left(g\right)\to MgC{l}_2\left(s\right)$