For which block is m(l) = -1 not allowed?

The value of the magnetic quantum number (mₗ) indicates the orientation of a subshell in space and is determined by the angular momentum quantum number (l). In quantum mechanics, the allowed values of mₗ range from -l to +l.

For the s block, which corresponds to an angular momentum quantum number (l) of 0, the only possible value of mₗ is 0. Therefore, since mₗ = -1 falls outside this range, it is not allowed in the s block.

In contrast, for the p block, where l = 1, the allowed values of mₗ are -1, 0, and +1. The d block has l = 2, permitting values of mₗ from -2 to +2, and the f block, with l = 3, allows values from -3 to +3. Thus, both the p, d, and f blocks have permissible values of mₗ that include -1, whereas the s block does not.