NDA (I) 2022 GAT Q61: Which one of the following is a covalent

Q: What is the answer to NDA (I) 2022 GAT Q61?

C. Correct — C, Silicon carbide. Silicon carbide (SiC) forms between two non-metals — silicon and carbon — which share electrons, making it a covalent compound (in fact a giant covalent network solid). The other three form between a metal and a non-metal by the transfer of electrons, so they are ionic: calcium oxide (CaO), sodium nitride (Na₃N) and zinc sulphide (ZnS).

NDA (I) 2022 General Ability Test · Question 61 of 150

Question text verified against the official NDA question paper.

Which one of the following is a covalent compound?

(a)Calcium oxide
(b)Sodium nitride
(c)Silicon carbide
(d)Zinc sulphide

Answer

Why

Correct — C, Silicon carbide. Silicon carbide (SiC) forms between two non-metals — silicon and carbon — which share electrons, making it a covalent compound (in fact a giant covalent network solid). The other three form between a metal and a non-metal by the transfer of electrons, so they are ionic: calcium oxide (CaO), sodium nitride (Na₃N) and zinc sulphide (ZnS).

Why the others are wrong

(a)Calcium oxide — Calcium (a metal) transfers electrons to oxygen (a non-metal), forming the ionic compound CaO, not a covalent one.
(b)Sodium nitride — Sodium is a reactive metal and nitrogen a non-metal, so they form the ionic compound Na₃N by electron transfer.
(d)Zinc sulphide — Zinc is a metal and sulphur a non-metal, so ZnS is essentially ionic (with some covalent character), not a typically covalent compound.

Concept

A covalent bond forms when two atoms share electrons, which typically happens between two non-metals. An ionic bond forms when a metal transfers electrons to a non-metal, producing charged ions. So the metal-plus-non-metal pairs are ionic, while the non-metal-plus-non-metal pair is covalent.

Scan each option for a metal. Calcium, sodium and zinc are metals, so their compounds with oxygen, nitrogen and sulphur are ionic. Silicon and carbon are both non-metals, so silicon carbide is the covalent compound.

Key facts

Covalent compounds form between two non-metals that share electrons.
Silicon and carbon are both non-metals, so silicon carbide (SiC) is covalent.
Metal-plus-non-metal combinations (CaO, Na₃N, ZnS) form ionic bonds by electron transfer.
Silicon carbide (carborundum) is a very hard covalent network solid used as an abrasive.

An iridescent crystalline lump of silicon carbide (carborundum), a very hard covalent abrasive — Silicon carbide, sold as carborundum, is a hard covalent network solid of the two non-metals silicon and carbon — used in grinding wheels and sandpaper.Image: Beeblaine · Wikimedia Commons (CC BY 4.0)

Study next

Ionic versus covalent bondingTelling metals from non-metals in a compoundGiant covalent (network) solids such as diamond and silicon carbideProperties of ionic and covalent compoundsElectronegativity and bond type

Common traps

Assuming any compound with a metal-sounding name is covalent.
Forgetting that a covalent bond forms between two non-metals.

Identify the compound made of two non-metals (silicon and carbon) — that is the covalent one, the rest being metal-plus-non-metal ionic compounds.

Related PYQs

No directly related past PYQ was found.

Practice

practice — not a real PYQ
Which one of the following is an ionic compound?
- (a)CO₂
- (b)NaCl
- (c)CH₄
- (d)HCl
Answer(b) NaCl — a metal (Na) combined with a non-metal (Cl).
practice — not a real PYQ
A covalent bond is formed by
- (a)transfer of electrons
- (b)sharing of electrons
- (c)loss of electrons only
- (d)gain of electrons only
Answer(b) sharing of electrons.