A reversible chemical reaction is said to be at DYNAMIC equilibrium when

1. NCERT §6.2 defines dynamic equilibrium: at equilibrium, BOTH the forward AND reverse reactions continue to occur, but their RATES are equal — so the macroscopic concentrations of all species remain constant. 2. The system is DYNAMIC because microscopic interconversion never stops; it's at equilibrium because the net rate of change is zero. 3. Option A describes the OBSOLETE static-equilibrium picture (one reaction "finishes"), which is not what is observed experimentally (NCERT's "Student's Activity" box on radioactively-labelled iodine confirms continuous interconversion). 4. Option C confuses equal RATES with equal CONCENTRATIONS — these are usually different. Option D is unrelated. _Source: NCERT Class 11 Chemistry, Ch 6 "Equilibrium", §6.2 (Equilibrium in Chemical Processes — Dynamic Equilibrium), p. 4–5._