Active absorption of mineral salts makes use of
A. Ionic exchange
B. Carriers
C. Phosphorylation of elements
D. None of the above

Hint: Active absorption of mineral salts involves the absorption of ions, with the use of metabolic energy. The lipid-protein membrane of the cell is permeable to the free ions, which helps in transport of free ions with the help of this energy across the membrane.

Complete answer:
Plants absorb minerals from the soil with the help of roots in the form of inorganic ions. Process of water absorption and mineral salt absorption are two different concepts. Plants absorb mineral salts from the soil which are dissolved in the water. Mineral salt absorption occurs through roots through the meristematic region of the root tip. There are two types of mineral absorption in the plants which are called active mineral absorption and passive mineral absorption.
Passive mineral absorption involves the passive process which does not require expenditure of metabolic energy. This absorption occurs along the concentration gradient by the process of simple diffusion.
Active mineral absorption is an active process of mineral absorption as it requires expenditure of metabolic energy in the form of ATP. Active absorption helps in mineral salt absorption both along and against the concentration gradient by osmosis or with help of special carrier proteins in the plasma membrane. Active absorption is more efficient compared to passive absorption.

Hence, the correct option is B. Carriers.

Note: Passive mineral absorption is a passive, physical and spontaneous process whereas active mineral absorption is an active, chemical and non spontaneous process. Rate of mineral absorption in active absorption depends on respiration.