The 1959 WHO International Standards for Drinking Water suggested that concentrations of copper greater than 1.5 mg/litre would markedly impair the potability of the water. However, in the first edition of the Guidelines for Drinking Water Quality, published in 1984, a guideline value of 1.0 mg/litre was established for copper, based on its laundry and other staining properties.

Correct Option: C

The 1959 WHO International Standards for Drinking Water suggested that concentrations of copper greater than 1.5 mg/litre would markedly impair the potability of the water. However, in the first edition of the Guidelines for Drinking Water Quality, published in 1984, a guideline value of 1.0 mg/litre was established for copper, based on its laundry and other staining properties.

Seventy percent of bone consists of hydroxyapatite, a calcium phosphate mineral (known as bone mineral). Tooth enamel is composed of almost ninety percent hydroxylapatite.

Correct Option: A

Seventy percent of bone consists of hydroxyapatite, a calcium phosphate mineral (known as bone mineral). Tooth enamel is composed of almost ninety percent hydroxylapatite.

An emulsion is a mixture of two liquids that cannot combine into a solution. In the case of milk, butterfat globules are suspended in a water-based fluid. The globules are encased in membranes that prevent them from combining into giant lumps of butterfat.

Correct Option: A

An emulsion is a mixture of two liquids that cannot combine into a solution. In the case of milk, butterfat globules are suspended in a water-based fluid. The globules are encased in membranes that prevent them from combining into giant lumps of butterfat.

Water is not effective on petrol fire because it has higher density than petrol as a result of which it sinks to the bottom, while petrol stays afloat and keeps burning. Petro-chemical fires are nearly always extinguished with chemical foam which forms a blanket over the flames and cuts off the oxygen supply.

Correct Option: D

Water is not effective on petrol fire because it has higher density than petrol as a result of which it sinks to the bottom, while petrol stays afloat and keeps burning. Petro-chemical fires are nearly always extinguished with chemical foam which forms a blanket over the flames and cuts off the oxygen supply.

Coal tar is a brown or black liquid of extremely high viscosity. In the coal gas era, there were many companies in Britain whose business was to distill coal tar to separate the higher-value fractions, such as naphtha, creosote and pitch. Naphthalene is derived from a kind of naphtha (a broad term encompassing any volatile, flammable liquid hydrocarbon mixture, including coal tar).

Correct Option: A

Coal tar is a brown or black liquid of extremely high viscosity. In the coal gas era, there were many companies in Britain whose business was to distill coal tar to separate the higher-value fractions, such as naphtha, creosote and pitch. Naphthalene is derived from a kind of naphtha (a broad term encompassing any volatile, flammable liquid hydrocarbon mixture, including coal tar).