Pakistan MCQs

Mass number applies to a specific isotope.
It is always a whole number.

Isotopes have the same atomic number but different mass numbers.
Their chemical behavior is usually similar.

Ions form by gaining or losing electrons.
Cations are positive and anions are negative.

A cation forms when electrons are lost.
It has more protons than electrons.

An anion forms when electrons are gained.
It has more electrons than protons.

Rutherford concluded that atoms contain a small dense positive nucleus.
Most atomic volume is empty space.

Particles equal moles times Avogadro's number.
0.5×6.022×10^23 = 3.011×10^23 molecules.

Moles equal particles divided by Avogadro's number.
1.2044×10^24 ÷ 6.022×10^23 = 2 mol.

Carbon contributes about 12 and two oxygens contribute 32.
The total molar mass is about 44 g/mol.

Oxygen contributes 16 of the 18 g/mol formula mass.
16/18×100 ≈ 88.9%.

The coefficients of H2 and H2O are equal.
Thus 4 mol H2 produce 4 mol H2O.

The mole ratio H2:NH3 is 3:2.
6 mol H2×2/3 = 4 mol NH3.