150 Units -> Using the price elasticity of supply formula: Es = [(Q2 - Q1)/Q1] / [(P2 - P1)/P1]. Substituting values: 2.5 = [(Q2 - 300)/300] / [(4 - 5)/5]. Solving: 2.5 = [(Q2 - 300)/300] / [-0.2]. This gives us: 2.5 × (-0.2) = (Q2 - 300)/300, so -0.5 = (Q2 - 300)/300. Therefore: Q2 - 300 = -150, which means Q2 = 150 units. When price falls by 20% (from Rs. 5 to Rs. 4), with elasticity of 2.5, quantity supplied falls by 50% (from 300 to 150 units). -> correct