The product obtained when $13$ is multiplied by $7$(in roman number ) is

The correct option is D XCI

$13\times 7=91$

Break the number $91$ (decompose it) into place value subgroups:

$91=90+1;$

Convert each subgroup: $90=100-10=>C-X=XC;1=I;$

Wrap up the Roman numeral:

$91=90+1=XC+I=XCI;$

$XCI$ is a group of numerals in additive and subtractive notation which will be $91.$

So option C is the correct answer.