. In which reaction is nitric acid acting as an oxidising agent? A. CuO + 2HNO3 → Cu(NO3)2 + H2O B. Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2 C. Na2CO3 + 2HNO3 → 2NaNO3 + H2O + CO2 D. NaOH + HNO3 → NaNO3 + H2O

B. Cu + 4HNO3 → Cu(NO3)2 + 2H2O

Explanation:

A redox reaction is one in which oxidation and reduction reactions are occuring simultaneously.

In a redox reaction, an oxidizing agent is reduced ( its oxidation state decreases) whereas a reducing agent is oxidized (it's oxidation state increases).

The nitrogen in the nitrate (v) ion, NO3-, exists in the +5 oxidation state. Therefore it would be acting as an oxidizing agent in any reaction in which it's oxidation state becomes less than +5 after the reaction.

Let us then consider each of the reactions:

A. Reaction 1: in this reaction, the oxidation state of nitrogen remains +5 as what is simply an exchange of radicals in a neutralization reaction.

B. Reaction 2: in this reaction, trioxocarbonate (v) acid oxidizes Copper atom to Copper (ii) ion, while itself it is reduced to Nitrogen (IV) oxide. The oxidation state of nitrogen changes from +5 to +4

C. Reaction 3: in this reaction, what occurs is an exchange of radicals by a displacement reaction. The oxidation state of nitrogen remains the same

D. Reaction 4: in the reaction, what occurs is a neutralization reaction, and the oxidation state of nitrogen remains the same.

Therefore, the correct option is B.

explanation:

the largest database of organic compounds lists about 10 million substances, which include compounds originating from living organisms and those synthesized by chemists. the number of potential organic compounds has been estimated at 1060—an astronomically high number. the existence of so many organic molecules is a consequence of the ability of carbon atoms to form up to four strong bonds to other carbon atoms, resulting in chains and rings of many different sizes, shapes, and complexities. the simplest organic compounds contain only the elements carbon and hydrogen, and are called hydrocarbons. even though they are composed of only two types of atoms, there is a wide variety of hydrocarbons because they may consist of varying lengths of chains, branched chains, and rings of carbon atoms, or combinations of these structures. in addition, hydrocarbons may differ in the types of carbon-carbon bonds present in their molecules. many hydrocarbons are found in plants, animals, and their fossils; other hydrocarbons have been prepared in the laboratory. we use hydrocarbons every day, mainly as fuels, such as natural gas, acetylene, propane, butane, and the principal components of gasoline, diesel fuel, and heating oil. the familiar plastics polyethylene, polypropylene, and polystyrene are also hydrocarbons. we can distinguish several types of hydrocarbons by differences in the bonding between carbon atoms. this leads to differences in geometries and in the hybridization of the carbon orbitals.

the answer is na (sodium)