Pakistan MCQs

Aluminium has a low density and good corrosion resistance.
Its alloys are widely used in aircraft.

High salt concentration lowers available water through osmosis.
Many spoilage microbes cannot grow well under these conditions.

Mercury remains liquid at typical room temperatures.
Its toxicity has reduced its use in household instruments.

Concentrated sugar binds water and creates high osmotic pressure.
This inhibits many microorganisms.

Pencil cores are made mainly of graphite mixed with clay.
Graphite is a form of carbon.

In graphite, each carbon forms three bonds and leaves mobile electrons.
These electrons carry charge along the layers.

Diamond and graphite are allotropes of carbon.
Their different structures give very different properties.

Each carbon atom bonds strongly to four others in diamond.
The rigid network resists deformation.

Chlorine in controlled amounts disinfects water.
It reduces disease-causing bacteria and viruses.

Polymers consist of repeating monomer units.
Many plastics, fibers, and biological molecules are polymers.

Calcium and magnesium ions cause hardness.
Hard water forms scale and reduces soap lather.

Strong polymer structures can resist decomposition.
This durability is useful but creates waste-management problems.