Option 1 states that one-third of the members of Rajya Sabha retire after every three years. This means that only a portion of the members retire after a fixed duration. However, the correct answer states that one-third of its members retire after every two years. This means that after every two years, one-third of the members step down from their positions in Rajya Sabha.

Option 2 suggests that two-thirds of the members retire after every three years. This statement contradicts the correct answer and is therefore incorrect.

Option 3 states that two-thirds of the members retire after every two years. This is different from the correct answer, which states that only one-third of the members retire after every two years. Hence, option 3 is incorrect.

Option 4 correctly states that one-third of the members retire after every two years. This means that every two years, one-third of the members of the Rajya Sabha step down from their positions. Since this matches the correct answer, option 4 is the correct statement.