Science MCQs

Calcium ion is Ca²⁺. Nitrate ion is NO₃⁻. Two nitrate ions are needed to balance the charge of one calcium ion: Ca(NO₃)₂.

Sulfur (S) is typically represented as S₈ not a diatomic molecule. N₂ O₂ and Cl₂ are diatomic.

Noble gases have stable electron configurations (full outer shells) and do not tend to gain lose or share electrons. Their combining capacity (valency) is zero.

Sodium has 11 electrons. The shell configuration is: K-shell=2 L-shell=8 M-shell=1.

Chlorine has 17 electrons. The shell configuration is: K-shell=2 L-shell=8 M-shell=7.

Carbon (atomic number 6) has an electronic configuration of 2 4. The 4 electrons in the outer shell are its valence electrons.

When an atom forms an ion it gains or loses electrons changing the total electron count. Na⁺ has lost 1 electron Cl⁻ has gained 1 O²⁻ has gained 2.

The valencies cross-multiply: Al³⁺ and O²⁻ becomes Al₂O₃.

Potassium ion is K⁺ (valency 1). Oxide ion is O²⁻ (valency 2). Two K⁺ ions balance one O²⁻ ion: K₂O.

HCl has a covalent bond but because chlorine is more electronegative the bond is polar (electrons are shared unequally).