There are two different isotopes; X and Y, both contain the same number of radioactive substances. If sample X has a longer half-life than Y, compare their rate of radioactive decay.
O A. Rate does not depend on half-life
B. Both of their rates are equal
O C. X has a smaller rate than Y
O D. X has a greater rate than Y

Half life refers to the time for 1/2 of the radioactive atoms to decay.

Suppose that X has a half life of 10 days and Y has a half life of 20 days

If both start out with 1000 radioactive atoms then after 20 days

X would have 250 radioactive atoms and Y would have 500 atoms

The rate of decay is greater for the shorter half life:

In the example given X  must have the smaller rate of decay because it has a longer half life.