Two radioactive materials A & B have decay constants 12X & X respectively . If initially they have same no.of nuclei , then ratio of no. of nuclei of A to B will be $\;\large\frac{1}{e}\;$ after a time

Question

$(a)\;1/12 X\qquad(b)\;1/11X\qquad(c)\;1/32X\qquad(d)\;1/224X$