Studies on a machine that molds plastic water pipe indicate that when it is injecting $2-$inch$-$diameter pipe, the process standard deviation is $0\mathrm{.}5$ inches. The $2-$inch pipe has a specification of $2$ inches plus or minus $0\mathrm{.}20$ inches. What is the process capability index $($Cp$)?$

Cannot determine

$0\mathrm{.}667$

$1\mathrm{.}0$

$2\mathrm{.}0$

$0\mathrm{.}1333$