Solubility in Water:
Water is often called the universal solvent because it has the ability to dissolve many substances. However, not all substances are soluble in water. The solubility of a substance depends on its chemical properties and the nature of its molecules.

Chloroform:
Chloroform (CHCl3) is a nonpolar compound. Nonpolar substances do not dissolve well in water because water is a polar solvent. In polar solvents like water, the positively charged regions attract the negatively charged regions of polar molecules, causing them to dissolve. Since chloroform is nonpolar, it is insoluble in water. Therefore, option 'a' is incorrect.

Benzene:
Benzene (C6H6) is a nonpolar compound, similar to chloroform. It consists of carbon and hydrogen atoms arranged in a hexagonal ring structure. Like chloroform, benzene is also insoluble in water due to its nonpolar nature. Thus, option 'b' is incorrect.

Phenol:
Phenol (C6H6O) is a polar compound. It contains a hydroxyl group (-OH) attached to a benzene ring. The presence of the hydroxyl group makes phenol partially soluble in water. However, phenol's solubility in water is limited because the benzene ring is still nonpolar. Therefore, option 'c' is incorrect.

Formic Acid:
Formic acid (HCOOH) is a polar compound. It contains a carboxyl group (-COOH), which is a combination of a hydroxyl group and a carbonyl group. The presence of the hydroxyl group makes formic acid soluble in water. The polar water molecules can interact with the hydroxyl group and form hydrogen bonds, allowing formic acid to dissolve. Hence, option 'd' is correct.

In summary, among the given options, only formic acid (option 'd') is soluble in water. Chloroform, benzene, and phenol are insoluble or only partially soluble in water due to their nonpolar or partially polar nature.