Which of the following is the maximum number of electrons that can be present in M-shell? A. 2 B. 8 C. 18 D. 32

The correct answer is C. 18.

The M-shell is the third shell in an atom, and it can hold up to 18 electrons. This is because each shell can hold up to 2n^2 electrons, where n is the shell number. The first shell (n=1) can hold up to 2 electrons, the second shell (n=2) can hold up to 8

Option A is incorrect because it is the number of electrons that can be held in the first shell.

Option B is incorrect because it is the number of electrons that can be held in the second shell.

Option D is incorrect because it is the number of electrons that can be held in the fourth shell.