Water: a precious resource - class-VII

Compounds can exist in all three states(solid, liquid, gas) provided that they can be heated/cooled enough(to their respective boiling/melting points). Thus water, ice, and steam all are compounds of hydrogen and oxygen.

The levelling effect refers to the inability of a solvent to distinguish between the strengths of strong acids or bases. Water is a leveling solvent for strong acids; however, the question asks where it is minimum. In non-leveling or differentiating solvents, the effect is minimized.

Water is made of Hydrogen and Oxygen, which are gases at STP. 

Dissolved salts in potable water provide taste and are useful for living being like calcium and magnesium ions.

$22^{nd}$ of March every year is celebrated as the world water day.

Burning hydrogen with oxygen give rise to formation of water.

Henry Cavendish showed that water is made up of hydrogen and oxygen.

The number of molecules of water is 5. The formula is $CuSO _4. 5H _2O$.

The colour of hydrated copper sulphate is blue.

Anhydrous cobalt(II) chloride is blue. When it reacts with water, it forms the hexahydrate complex CoCl2.6H2O, which is pink.

The colour of anhydrous copper sulphate is white.

Approximately 97 percent of Earth's water is saline, found in the oceans. Among the options provided, 93.7 percent is the closest accepted value in many textbooks.

The earth appears blue from outer space because 70% of the earth's surface contains water, i.e., water bodies like oceans, seas, rivers, lakes, etc.

The property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of its molecules is called surface tension. while washing clothes, detergents reduce the surface tension of the water molecule which causes the formation of foam and cleaning of clothes. 

Hard water contains chlorides, carbonates and bicarbonates of sodium and magnesium ions which combine with soap micelles and do not give lather with soap.

The number of molecules of water in $CoCl _2$ is 6. So the formula becomes $CoCl _2.6H _2O$.

Rain water and distilled water does not contain impurities.

Dissolved salts in water are important because
(A) They provide taste
(B) Growth of plants
(C) Minerals essential for body
Water contains dissolved salts which provide taste to water for drinking purposes. Also these salts are essential for growth and development of plants. These dissolved salts provide the essential minerals which are required for growth of body.

Dissolved gases can be removed from water by boiling.
Water contains certain gases in dissolved state. The higher the temperature of a solution becomes, the less a gas dissolves provided it doesn't react with the solvent. Consequently, heating/boiling a solution can expel the remaining gas.

Anhydrous $CoCl _2$ is blue in colour.

The gas-phase oxidation of hydrogen has been extensively studied over a wide range of temperatures and pressures.