The correct answer is option 4 - Statement-I is incorrect but Statement-II is correct.

Statement-I suggests that one of the standard sizes of the National Flag of India is 600 mm x 400 mm. It is not accurate because, while the flag does have defined sizes according to the Flag Code of India, 600 mm x 400 mm is not one of them.

Statement-II, on the other hand, suggests that the ratio of the length to the height (width) of the Flag shall be 3:2. This statement is accurate. The aspect ratio of the flag is indeed 3:2, meaning the flag`s length is 1.5 times its height. This ratio gives the National Flag of India its distinctive shape. Since this fact does not explain the size of the flags, it is not the correct explanation for Statement-I.