Pakistan MCQs

Valence electrons largely determine chemical reactivity.
Elements in a group often share similar valence configurations.

Thomson's cathode-ray experiments revealed negatively charged particles.
He proposed an early model with electrons in positive matter.

Periodic trends arise from repeating valence-shell patterns.
The periodic table organizes these regularities.

Chadwick identified the neutral nuclear particle in 1932.
Neutrons explain isotopic mass differences.

Alkali metals have one valence electron.
They commonly form +1 ions and are highly reactive.

Atomic number identifies the element.
In a neutral atom it also equals the number of electrons.

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

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.