The electron configuration of Cr (24) is given as [Ar] 4s1 3d5. In order to determine the number of electrons with l = 1 and l = 2, we need to understand the quantum numbers and their significance.

Quantum numbers:
- Principal quantum number (n) represents the energy level or shell of an electron.
- Azimuthal quantum number (l) represents the shape of the electron's orbital.
- Magnetic quantum number (m) represents the orientation of the orbital in space.
- Spin quantum number (s) represents the spin of the electron.

Electrons with l = 1:
The azimuthal quantum number (l) can have integral values ranging from 0 to n-1, where n is the principal quantum number. In this case, the principal quantum number (n) for Cr (24) is 3. Therefore, the possible values of l are 0, 1, and 2.

- For l = 1, there is only one possible value, which corresponds to the 3d orbital. The 3d orbital can hold a maximum of 10 electrons. However, in this case, we are considering the number of electrons with l = 1, which is only one. Therefore, the number of electrons with l = 1 is 1.

Electrons with l = 2:
Similarly, for l = 2, there are two possible values, which correspond to the 4s and 4p orbitals. The 4s orbital can hold a maximum of 2 electrons, and the 4p orbital can hold a maximum of 6 electrons.

- For l = 2, there is one electron in the 4s orbital (as given in the electron configuration [Ar] 4s1) and five electrons in the 3d orbital (as given in the electron configuration [Ar] 3d5). Therefore, the total number of electrons with l = 2 is 1 (from 4s) + 5 (from 3d) = 6.

Therefore, the correct answer is option B: 12 electrons with l = 1 and 5 electrons with l = 2.