Functional groups

Ethanol contains a hydroxyl (–OH) group whose hydrogen can be displaced by a sufficiently reactive metal such as sodium. The reaction is 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂. Thus sodium ethoxide is formed and hydrogen gas is released. Carbon dioxide is associated with combustion or reactions involving carbonates, oxygen is not the product here, and chlorine is unrelated.

The governing concept is that a functional group is the atom or group of atoms responsible for the characteristic chemical behaviour of an organic compound. Carboxylic acids contain the –COOH group, called the carboxyl group. It combines a carbonyl group (C=O) with a hydroxyl group (–OH), but the complete –COOH group gives the acid its identity. Therefore option A is correct; hydroxyl alone represents alcohols, while a double bond or halogen is not the defining group here.

The governing concept is that the functional group controls the characteristic reactions of a carbon compound. For example, an –OH group gives alcohols their typical reactions, –COOH gives carboxylic acids acidic behaviour, and a C=C bond allows addition reactions in alkenes. The carbon skeleton may remain similar while changing the functional group changes chemical properties substantially. Therefore option A is correct; colour, mass reduction, and metallic character are not its defining functions.

Systematic naming begins by identifying the parent carbon chain, usually the longest continuous chain containing the principal functional group. Its number of carbon atoms gives the root name, such as meth-, eth-, or prop-. The functional group determines the suffix and the compound’s class, for example -ol for an alcohol or -oic acid for a carboxylic acid. Colour, smell, and mass do not establish the IUPAC name, so A is correct.

Geographical isolation separates populations by barriers such as mountains, rivers, or distance and reduces gene flow between them. Because each group faces its own mutations, variations, selection pressures, and environmental conditions, different changes can accumulate over generations. Reproductive differences may eventually lead to speciation, so option A is correct. Isolation does not make organisms instantly identical, erase chromosomes, or always remove food.

The governing concept is the structural and functional organisation of the excretory system. Each nephron performs the essential stages of urine formation: filtration of blood at the glomerulus, selective reabsorption of useful water and solutes, and secretion of some wastes into the tubule. Because these processes together carry out the kidney’s basic filtering function, the nephron is called its functional unit. Thus option A is correct; the other options describe digestive, respiratory, or plant functions.