Select the set in which the numbers are related in the same way as are the numbers of the following sets.
(NOTE : Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 – Operations on 13 such as adding / subtracting / multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)
(6, 11, 19)
(7, 12, 21)

Given: 

(6, 11, 19)
(7, 12, 21)

Logic: (1st number + 2nd number) + 2 = 3rd number

For, (6, 11, 19)

6 + 11 = 17, 17 + 2 = 19

For, (7, 12, 21)

7 + 12 = 19, 19 + 2 = 21

Now, we check each options.

Option (a): (8, 13, 29) (Not Follow)

8 + 13 = 21, 21 + 2 $$\neq$$ 29​

​Option (b): (17, 23, 43) (Not Follow)​

17 + 23 = 40, 40 + 2 $$\neq$$ 43​

Option (c): (12, 17, 31) (Follow)​

12 + 17 = 29, 29 + 2 = 31

Option (d): (10, 5, 7) (Not Follow)​

10 + 5 = 15, 15 + 2 $$\neq$$ 7​

Thus, correct option is (c).