Which one of the following is the correct order of the valencies of elements Ne, Si, N and Mg?
- (a)Ne < Mg < N < Si
- (b)Si < N < Mg < Ne
- (c)Ne < N < Si < Mg
- (d)Mg < Ne < N < Si
Correct — A, Ne < Mg < N < Si. Valency is the combining capacity of an element. Neon (Ne) is a noble gas with a complete outer shell, so its valency is 0. Magnesium (Mg) has 2 outer electrons, giving valency 2. Nitrogen (N) has 5 outer electrons and commonly shows valency 3 (8 − 5). Silicon (Si) has 4 outer electrons, giving valency 4. Arranged in increasing order this is Ne (0) < Mg (2) < N (3) < Si (4).
- (b)Si < N < Mg < Ne — This is the exact reverse — it puts silicon (valency 4) lowest and neon (valency 0) highest, but neon's valency is the smallest, not the largest.
- (c)Ne < N < Si < Mg — Neon is rightly lowest, but the rest are out of order: nitrogen (3) and silicon (4) are placed below magnesium (2), which is wrong.
- (d)Mg < Ne < N < Si — This puts magnesium (valency 2) below neon, but neon's valency is 0 — the smallest of all — so neon must come first.
Valency is the number of electrons an atom gains, loses or shares to complete its outer shell. It can be read from the group / number of valence electrons: elements with 1–4 outer electrons usually have that number as their valency, while for 5–7 the valency is 8 minus the number of outer electrons, and a full shell (noble gas) gives valency 0.
Assign each element's valency from its outer electrons: Ne (full shell) = 0, Mg = 2, N = 3 (8 − 5), Si = 4. Ordering these from smallest to largest gives Ne < Mg < N < Si. The key is remembering that a noble gas has valency 0, not a high value.
- Valency is the combining capacity — electrons gained, lost or shared to complete the outer shell.
- Noble gases such as neon have a full outer shell, so their valency is 0.
- Magnesium (2 outer electrons) has valency 2; silicon (4 outer electrons) has valency 4.
- Nitrogen has 5 outer electrons and a common valency of 3 (8 − 5).
Increasing valency: Ne (0) < Mg (2) < N (3) < Si (4) — option (a).
- Assuming a noble gas has a high valency because it is stable — its valency is actually 0.
- Reading nitrogen's valency as 5 instead of its usual 3.
Assign each element's valency from its outer electrons, then order them — the noble gas (neon) is always lowest at 0.
No directly related past PYQ was found.
- practice — not a real PYQ
The valency of a noble gas such as argon or neon is
- (a)0
- (b)1
- (c)2
- (d)8
Answer(a) 0 — its outer shell is already complete.
- practice — not a real PYQ
The valency of magnesium (electronic configuration 2, 8, 2) is
- (a)1
- (b)2
- (c)3
- (d)4
Answer(b) 2 — it loses its 2 outer electrons.