What is the maximum number of electrons in the M-Shell?
- (a)6
- (b)8
- (c)18
- (d)32
Correct — C, 18. The maximum number of electrons a shell can hold is given by 2n², where n is the shell number. The M-shell is the third shell, so n equals 3 and its capacity is 2 × 3² = 2 × 9 = 18 electrons. By the same rule the K-shell (n = 1) holds 2 and the L-shell (n = 2) holds 8, so 18 is the M-shell value.
- (a)6 — No shell has a maximum capacity of 6; applying 2n² to the M-shell gives 18.
- (b)8 — 8 is the capacity of the L-shell (n = 2), not the M-shell.
- (d)32 — 32 is the capacity of the N-shell (n = 4), one shell beyond the M-shell.
Electrons in an atom are arranged in shells labelled K, L, M, N for n = 1, 2, 3, 4. The maximum number of electrons that a shell can hold is 2n², so the capacity rises as the shell number increases.
Map the letters to numbers, with K, L, M, N standing for n = 1, 2, 3, 4, then apply 2n² for the shell in question. The M-shell is n = 3, which gives 18.
- The maximum electrons in a shell is 2n², where n is the shell number.
- The K, L, M and N shells correspond to n = 1, 2, 3 and 4.
- Their capacities are 2, 8, 18 and 32 electrons respectively.
- The outermost shell of an atom, however, cannot hold more than 8 electrons (the octet limit).
Applying 2n², the M-shell (n = 3) holds a maximum of 18 electrons.
- Confusing the M-shell (18) with the L-shell (8) or the N-shell (32).
- Applying the octet limit of 8 as the M-shell's total capacity.
Asked for a shell's maximum electrons; apply 2n² with the M-shell as n = 3.
No directly related past PYQ was found.
- practice — not a real PYQ
The maximum number of electrons in the L-shell is
- (a)2
- (b)8
- (c)18
- (d)32
Answer(b) 8 — 2n² with n = 2.
- practice — not a real PYQ
According to the 2n² rule, the N-shell can hold at most
- (a)8
- (b)18
- (c)32
- (d)50
Answer(c) 32 — 2n² with n = 4.