Explanation:

- The dishonest shopkeeper sells onions at the cost price of Rs. 30 per kg but gives only 750g instead of 1 kg.

- For 2 kg, instead of giving 2000g, he gives only 1500g.

- The effective cost of 1500g = Rs. 60, i.e., Rs. 30/kg for 2 kg.

- The actual amount provided is 1.5 kg at Rs. 60 which makes the effective rate Rs. 40/kg (60/1.5).

- Cost price = Rs. 30/kg, effective selling price = Rs. 40/kg.

- Profit per kg is Rs. 40 - Rs. 30 = Rs. 10.

- Profit percentage = (Profit/Cost Price) × 100 = (10/30) × 100 = 33.33%.

The correct option is:

- Option 4: 33.33%