Elements P, Q, R, S have 6, 11, 15, 17 electrons respectively, therefore,

Step 1: Analyze the question We need to work out the electron configuration of each element, then decide what type of bond forms between the pairs in the options.

Step 2: Electron configurations

• P (6 electrons): 2, 4. Four valence electrons, so it is carbon, a non-metal.
• Q (11 electrons): 2, 8, 1. One valence electron, so it is sodium, a metal.
• R (15 electrons): 2, 8, 5. Five valence electrons, so it is phosphorus, a non-metal.
• S (17 electrons): 2, 8, 7. Seven valence electrons, so it is chlorine, a non-metal.

Step 3: The concept

• Electrovalent (ionic) bond: forms between a metal and a non-metal, by transfer of electrons.
• Covalent bond: forms between two non-metals, by sharing of electrons.

Step 4: Check each option

• A. P with R: carbon and phosphorus are both non-metals, so the bond is covalent, not electrovalent. Wrong.
• B. Q with S: sodium (a metal) and chlorine (a non-metal) transfer electrons, so the bond is ionic, not covalent. Wrong.
• C. R with S: phosphorus and chlorine are both non-metals, so they share electrons (covalent, as in PCl₃). Wrong.
• D. Q with S: sodium gives its 1 valence electron to chlorine, forming Na⁺ and Cl⁻. This is an electrovalent bond (NaCl). Correct.

Answer: D

Exam tip: Convert the electron count to a configuration quickly (2, 8, 8…). Then ask whether the element is a metal (1–3 valence electrons) or a non-metal (4–7). Metal + non-metal gives ionic, and non-metal + non-metal gives covalent. Group 1 with Group 7 is the classic ionic pair.