Consider the following minerals: 1. Calcium 2. Iron 3. Sodium Which of the minerals given above is/are required by human body for the contraction of muscles?

All three minerals contribute, so the answer is D. Calcium is the central trigger: when a motor neuron fires, Ca2+ is released from the sarcoplasmic reticulum, binds troponin, shifts tropomyosin off the actin binding sites, and lets myosin cross-bridges form. Relaxation follows when calcium is pumped back.

Sodium is needed to generate the action potential across the sarcolemma that triggers this calcium release, so it is indirectly essential for every contraction. Iron is a component of myoglobin, which stores and delivers oxygen to working muscle fibres; without it, sustained contraction fails. Option A ignores the other two, B wrongly excludes calcium, and C wrongly excludes iron.

Core concept: excitation-contraction coupling, with calcium as the trigger and sodium as the electrical carrier. For Mains, this links to nutrition, deficiency disorders (anaemia, tetany from hypocalcaemia) and public health programmes.

Trap: aspirants pick A because calcium is the obvious muscle mineral, forgetting that sodium drives the action potential and iron supports oxygen supply to muscle.