The bonding pair of electrons in a Hydrogen Chloride molecule is pulled towards the chlorine atom because

Step 1: Analyze the question The question asks why the shared (bonding) pair of electrons in HCl is drawn closer to chlorine than to hydrogen. This is about the polarity of a covalent bond.

Step 2: The concept When two different atoms share electrons in a covalent bond, the electrons are not shared equally. The atom with the greater electronegativity (the ability to attract the shared pair of electrons) pulls the pair closer to itself.

• Chlorine electronegativity ≈ 3.0 (Pauling scale)
• Hydrogen electronegativity ≈ 2.1

Step 3: Solution

• Chlorine has 17 protons and a high effective nuclear charge, so it attracts the bonding pair strongly.
• Hydrogen has only 1 proton and a weaker pull.
• As a result, the electron pair shifts towards Cl. Chlorine becomes slightly negative (δ⁻) and hydrogen slightly positive (δ⁺), so we write H^δ⁺–Cl^δ⁻. This is a polar covalent bond.

Checking the other options:

• A. Larger atomic size: Size does not cause the pull. A larger atom actually tends to be less electronegative, because the nucleus is farther from the bonding electrons.
• B. Larger atomic mass: Mass has no effect on how strongly electrons are attracted.
• D. No bonding orbitals within hydrogen: This is false. Hydrogen's 1s orbital overlaps with chlorine's 3p orbital to form the bond.

Answer: C. chlorine is more electronegative

Exam tip: When you see "electron pair pulled towards one atom," think electronegativity. Remember the trend: electronegativity increases across a period and decreases down a group, and fluorine is the most electronegative element.