How many different values of ml are possible in the 2p sublevel?

There are four quantum numbers for an orbital, namely, principal quantum number n, azimuthal quantum number l, magnetic quantum number and spin quantum number s. No two orbitals can have same value for all the four quantum numbers.

Principal quantum number tells about the position of orbital that is shell number, azimuthal quantum number describes the shape of orbital, for s, p, d, f,... orbitals, the value is 0, 1, 2, 3,... so on. The value of magnetic quantum number varies from -l to +l (including zero), it defines the sub shell of electron. Spin of the electron defines its movement that is clockwise or anticlockwise thus, there are only two possible values for spin quantum number: +1/2 or -1/2.

For 2p orbital, principal quantum number n is 2 (denotes the shell) and azimuthal quantum number for p orbital is 1. Thus, different values for magnetic quantum number will be -l to l that is -1, 0,1.

Therefore, for 2p subshell there are 3 different  values.

c. 75.7

i think that is the right

it's c. elements are placed in rows based on how may valencies electrons have.