Pakistan MCQs

Heterogeneous mixtures contain distinguishable regions or phases.
Examples include sand in water and granite.

A physical change alters form or state without changing chemical identity.
Ice and liquid water are both H2O.

Rusting forms new iron oxide substances.
Chemical changes involve rearrangement of atoms and new products.

Density describes how much mass is packed into a volume.
It is commonly expressed in g/cm³ or kg/m³.

The mole is the SI base unit for amount of substance.
One mole contains Avogadro's number of specified entities.

Avogadro's constant gives the number of entities in one mole.
The entities may be atoms, molecules, ions, or formula units.

Molar mass is numerically related to relative atomic or molecular mass.
Its common unit is g/mol.

An empirical formula shows the lowest integer ratio of elements.
It may differ from the molecular formula.

A molecular formula is a whole-number multiple of the empirical formula.
It applies to substances composed of discrete molecules.

Balancing follows conservation of atoms and mass.
Coefficients change amounts, not chemical formulas.

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.