Pakistan MCQs

After three half-lives, the remaining fraction is (1/2)^3=1/8.
800/8 = 100 nuclei.

Photoelectric emission requires photon energy above the material's work function.
Increasing intensity mainly increases the number of emitted electrons.

Twelve hours equals two half-lives.
The remaining fraction is (1/2)^2 = 1/4.

The work function depends on the material and surface condition.
Photoelectric emission begins when photon energy reaches this threshold.

Matter waves link momentum with wavelength through λ=h/p.
The effect is important at microscopic scales.

Bound atomic electrons occupy quantized energy states.
Transitions between levels involve photon absorption or emission.

Isotopes have the same atomic number and chemical identity.
Their mass numbers differ because neutron counts differ.

Radioactive decay is a nuclear process.
Its probability is characterized by a decay constant and half-life.

After each half-life, the number of undecayed nuclei halves.
The process is statistical and exponential.

Percentage yield = actual yield ÷ theoretical yield × 100.
(15 ÷ 20) × 100 = 75%.

The balanced equation fixes the required mole ratio.
Comparison of available amounts shows that O₂ is consumed first.

The balanced equation fixes the required mole ratio.
Comparison of available amounts shows that N₂ is consumed first.