the correct question is
how many times as large is the approximate radius of a mercury atom, 1.50*10^-11 meter, as the approximate radius of a hydrogen atom, 2.5*10^-11
Since both are conveniently --------> *10^-11
we can just divide 2.5 by 1.5
2.5/1.5-------> 1.6666
So a hydrogen atom is 1.67 times larger than a mercury atom