**(i)** Directly proportional.

**Explanation: **In this table value of ‘b’ is thrice the value of ‘a’ in all the columns. Therefore ‘a’ and ‘b’ are directly proportional.

**(ii)** Directly proportional.

**Explanation:** In this table value of ‘b’ is half of the value of ‘a’ in all the the columns. Therefore ‘a’ and ‘b’ are directly proportional.

**(iii) **Not directly proportional.

**Explanation: **In this table value of ‘b’ is not thrice the value of ‘a’ in all the columns. Therefore ‘a’ and ‘b’ are not directly proportional.

**(iv)** Not directly proportional.

**Explanation: **In this table value of ‘b’ is not varying in the same ratio as the value of ‘a’ in all the columns. Therefore ‘a’ and ‘b’ are not directly proportional.