If the principal quantum number is n = 3, what are the name(s) of the subshells? S
sp
spd
spdf

The name(s) of the subshells are s,p and d

Each orbital in an atom consists of 4 quantum numbers  

n is the principal quantum number.  

l is the angular momentum / azimuthal quantum number  

ml, the magnetic quantum number  

ms, the electron-spin quantum number  

Value of n: positive integer  

value of l: s = 0, p = 1, d = 2, f = 3 , ..(n-1)

ml value: between -l to + l  

ms value: +1/2 or -1/2  

n=3, then the possible value of l is a maximum of n-1 = 3-1 = 2

So the value of subshells = 0,1 and 2