How many subshells are there in the n = 4 principal shell? how many subshells are there in the n = 4 principal shell? 1 2 3 4 not enough information?

number of shubshell is equal to principle quantum number
n=1 -- 1 subshell 
n= 2--- 2 subshell 
n= p p subhshell similarly n=4 --- 4 subshells i.e 4s 4p 4d 4f

D=m/v =57.9/3 = 19.3 g/cm^3

The answer is c.  h+  and oh−  react to form water (h2o). i just took the test and i got it right. hope this !