When both the demand and supply curves shift to indicate an increase in demand and supply in the same proportion. Then:

Equilibrium price remains unchanged but equilibrium quantity increases.

The correct answer is Option (4) → Equilibrium price remains unchanged but equilibrium quantity increases.

When both demand and supply increase by the same proportion, the rightward shift of both curves leads to:

• Equilibrium price staying the same, because the increase in demand is exactly matched by the increase in supply.

• Equilibrium quantity increasing, since more of the good is both demanded and supplied at the same price.

Hence, the price stays unchanged, but the quantity traded increases.