This video states number of electrons in a atom having quantum numbers n=3, l=1.According to quantum mechanics, orbitals are characterised by nil,ml values.
n- principal quantum number
l- azimuthal quantum number
m-l - magnetic quantum number
For
n=1
possible values of I=0 & ml -0
n=2
possible values of I=0,1, ml = -1, 0, +1
n=3
possible values of I=0,1,2, ml= -2,-1,0, +1,+2
if l=o, it is s orbital which can hold only two electrons.