Pakistan MCQs

Percent yield is actual divided by theoretical times 100.
8/10×100 = 80%.

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

Mass percent expresses composition on a mass basis.
All component mass percentages sum to 100%.

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

Mole ratios convert amounts of one substance into another.
They come directly from the balanced equation.

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

Chemical reactions rearrange atoms but do not create or destroy them.
Therefore total mass remains constant in a closed system.

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

A pure compound has constant composition.
This is also called the law of constant composition.

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

Percent composition is calculated from formula mass contributions.
The element percentages sum to approximately 100%.

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