Le Chatelier's principle states that if a system at equilibrium is disturbed by a change in conditions, the equilibrium will shift in the direction that tends to counteract the disturbance. Increasing the concentration of a reactant (SO_2) provides more reactant molecules, so the forward reaction is favoured to consume the excess, shifting equilibrium right and producing more SO_3. Option A (increasing temperature) is wrong because the forward reaction is exothermic; raising temperature favours the endothermic reverse reaction, shifting equilibrium left and decreasing SO_3 yield. Option B (decreasing total pressure) is wrong because the forward reaction has fewer moles of gas on the product side (2 moles products vs 3 moles reactants), so decreasing pressure favours the reverse (higher mole) direction, shifting equilibrium left. Option C (adding inert gas at constant volume) does not change the partial pressures of any reactant or product and therefore has no effect on the position of equilibrium. This is a standard NCERT Le Chatelier application problem and a frequent JEE Main question. Plausibility check: only adding SO_2 directly increases the reaction quotient Q relative to K_c, driving the reaction forward.