Atomic Mass of Oxygen = 16g

Atomic Mass of Carbon = 12g

Atomic Mass of Sodium = 23g

Molecular Mass of Sodium Carbonate = [23×2] + [12×1]+[16×3]

= 46 + 12 + 48

= 106g

1 mole of Na₂CO₃ = 106 g

0.5 mole of Na₂CO₃ = X g

X = [0.5×106]/1

= 53g of Na₂CO₃

0.5M of Na₂CO₃ signifies 0.5 moles of Na₂CO₃ dissolved in 1 litre of water or rather 53g of Na₂CO₃ dissolved in 1 litre of water.