Element X forms a chloride with the formula XCl2, which is a solid with high melting point. X would most likely be in the same group of periodic table as
- (a)Na
- (b)Al
- (c)Mg
- (d)K
Answer
Why
Correct — C, Mg. A chloride of formula XCl2 means X combines with two chlorine atoms, so X is divalent — its valency is 2. A high-melting-point solid chloride points to an ionic metal chloride. Magnesium forms MgCl2 and belongs to Group 2 (the alkaline-earth metals), so X most likely shares magnesium's group.
Why the others are wrong
- (a)Na — Sodium is in Group 1 and is monovalent; it forms NaCl (formula XCl, not XCl2), so it cannot be X's group.
- (b)Al — Aluminium is in Group 13 and is trivalent, forming AlCl3 — that is XCl3, not XCl2.
- (d)K — Potassium, like sodium, is a Group 1 monovalent metal forming KCl (XCl); it does not match the XCl2 formula.
Concept
The formula of a chloride reveals the metal's valency: XCl gives a valency of 1, XCl2 a valency of 2, and XCl3 a valency of 3. Group 2 (alkaline-earth) metals such as magnesium and calcium are the divalent ones.
Work backward from the formula. Two chlorines mean valency 2, which is the alkaline-earth signature, and only magnesium among the four options is a Group 2 metal.
Key facts
- XCl2 implies a valency of 2, characteristic of Group 2 (alkaline-earth) metals.
- Magnesium (MgCl2) is a Group 2 metal, as are calcium, strontium and barium.
- Group 1 metals such as Na and K are monovalent (XCl); Group 13 aluminium is trivalent (XCl3).
- A high-melting solid chloride indicates ionic bonding between a metal and chlorine.
XCl2 means valency 2 — the alkaline-earth signature — so X is in magnesium's group (c).
Study next
Common traps
- Reading XCl2 as valency 1 or 3 instead of 2.
- Picking a Group 1 metal (Na or K) that would give XCl, not XCl2.
Given a chloride formula, deduce the element's valency and hence its periodic-table group.
Related PYQs
Which one among the following has valency of 3?
- (a) Carbon
- (b) Oxygen
- (c) Nitrogen
- (d) Sodium
Answer(c) Nitrogen
Same core skill — determining an element's valency. There you pick the trivalent element directly; here you infer valency 2 from the chloride formula XCl2 and place X in magnesium's group.
Practice
- practice — not a real PYQ
An element M forms an oxide M2O3. Its valency is
- (a)1
- (b)2
- (c)3
- (d)4
Answer(c) 3 — M2O3 corresponds to a valency of 3, like aluminium. - practice — not a real PYQ
Which of the following elements is divalent (valency 2)?
- (a)Sodium
- (b)Potassium
- (c)Calcium
- (d)Aluminium
Answer(c) Calcium — a Group 2 alkaline-earth metal.