Question

How many plane of symmetry does the $C{H}_4$ molecule contain?

Answer 1

$C{H}_4$ is a tetrahedral molecule. Pick any two hydrogen atoms. If we have a plane passing through the central carbon and the two selected hydrogen atoms, you'll see that this bisects the molecule into symmetrical halves. We could pick any two out of the four possible hydrogens in ${}^4{C}_2$ ways. Hence, the number of planes of symmetry = ${}^4{C}_2=6$.