There are a number of atmospheric gases which make up air. In the lower atmosphere or troposphere, the main gases are nitrogen and oxygen, which make up 78% and 21% of the volume of air respectively. The remaining 1% of the atmospheric gases is made up of trace gases.

Correct Option: D

There are a number of atmospheric gases which make up air. In the lower atmosphere or troposphere, the main gases are nitrogen and oxygen, which make up 78% and 21% of the volume of air respectively. The remaining 1% of the atmospheric gases is made up of trace gases.

Ionic compounds are made up of a metal and nonmetal, and covalent compounds are made up of two nonmetals. In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a central carbon atom by single covalent bonds: CH₄ + 4Cl₂ ? CCl<0sub>4 + 4HCl

Correct Option: D

Ionic compounds are made up of a metal and nonmetal, and covalent compounds are made up of two nonmetals. In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a central carbon atom by single covalent bonds: CH₄ + 4Cl₂ ? CCl<0sub>4 + 4HCl

In theory, a candle is made of a solid hydrocarbon called paraffin. When the solid burns, the hydrocarbon reacts with oxygen to form carbon dioxide and water. The reaction is exothermic, meaning it releases heat to the atmosphere along with the other products.

Correct Option: D

In theory, a candle is made of a solid hydrocarbon called paraffin. When the solid burns, the hydrocarbon reacts with oxygen to form carbon dioxide and water. The reaction is exothermic, meaning it releases heat to the atmosphere along with the other products.

Democritus first suggested the existence of the atom, but John Dalton (1766-1844) is credited with the Atomic Theory of Matter. According to Dalton, all matter is made of atoms; atoms are indivisible and indestructible; all atoms of a given element are identical in mass and properties; and compounds are formed by a combination of two or more different kinds of atoms.

Correct Option: B

Democritus first suggested the existence of the atom, but John Dalton (1766-1844) is credited with the Atomic Theory of Matter. According to Dalton, all matter is made of atoms; atoms are indivisible and indestructible; all atoms of a given element are identical in mass and properties; and compounds are formed by a combination of two or more different kinds of atoms.

Air is not the "ideal" breathing mixture for diving as with a concentration of approximately 79 percent nitrogen, compressed air poses two potential problems for all divers: susceptibility to nitrogen narcosis and at deeper depths; and decompression sickness. So divers use Nitrox, a gaseous mixture of nitrogen and oxygen. It is also known as ‘Enriched Air.’

Correct Option: B

Air is not the "ideal" breathing mixture for diving as with a concentration of approximately 79 percent nitrogen, compressed air poses two potential problems for all divers: susceptibility to nitrogen narcosis and at deeper depths; and decompression sickness. So divers use Nitrox, a gaseous mixture of nitrogen and oxygen. It is also known as ‘Enriched Air.’