To solve this problem, we need to determine the total number of boys in the row by analyzing the given information.

Given Information:
- Srinath is 7th from the left.
- Venkat is 12th from the right.
- When Srinath and Venkat interchange their positions, Srinath becomes 22nd from the left.

Let's break down the solution into steps:

Step 1: Determine Srinath's position in the original row
Srinath is 7th from the left, which means there are 6 boys to his left. We can represent this as:
_ _ _ _ _ _ Srinath

Step 2: Determine Venkat's position in the original row
Venkat is 12th from the right, which means there are 11 boys to his right. We can represent this as:
Venkat _ _ _ _ _ _ _ _ _ _ _

Step 3: Determine the total number of boys in the original row
To find the total number of boys in the row, we need to add the number of boys to the left of Srinath and the number of boys to the right of Venkat, along with Srinath and Venkat themselves. So the total number of boys in the original row can be calculated as:
6 + 1 + 11 = 18

Step 4: Determine Srinath's position in the new row after interchanging
After Srinath and Venkat interchange their positions, Srinath becomes 22nd from the left. This means there are 21 boys to his left. We can represent this as:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Srinath

Step 5: Determine the total number of boys in the new row
To find the total number of boys in the new row, we need to add the number of boys to the left of Srinath in the new row and Srinath himself. So the total number of boys in the new row can be calculated as:
21 + 1 = 22

Step 6: Compare the total number of boys in the original and new rows
We have determined that the total number of boys in the original row is 18 and in the new row is 22. Since Srinath's position has changed, the total number of boys must have changed as well. Therefore, there must be more boys in the new row compared to the original row.

Step 7: Determine the additional number of boys in the new row
To find the additional number of boys in the new row, we subtract the total number of boys in the original row from the total number of boys in the new row. So the additional number of boys in the new row can be calculated as:
22 - 18 = 4

Step 8: Determine the final number of boys in the row
Since the additional number of boys in the new row is 4, we add this to the total number of boys in the original row to find the final number of boys in the row. So the final number of boys in the row can be calculated as:
18 + 4 = 22

Therefore, the correct answer is option 'C', which states that there are 33 boys in the row.