Correct Answer: ×, −, ÷, +

Solution : Given:
21 * 3 * 36 * 2 * 23 = 68

Let's check the given options –
First option: ÷, −, ×, +
⇒ 21 ÷ 3 − 36 × 2 + 23 = 68
Solving the L.H.S. of the equation –
= 7 − 36 × 2 + 23
= 7 − 72 + 23
= −42 ≠ 68
Second option: ÷, ×, +, −
⇒ 21 ÷ 3 × 36 + 2 − 23 = 68
Solving the L.H.S. of the equation –
= 7 × 36 + 2 − 23
= 252 + 2 − 23
= 231 ≠ 68
Third option: +, ×, −, ÷
⇒ 21 + 3 × 36 − 2 ÷ 23 = 68
Solving the L.H.S. of the equation –
= 21 + 3 × 36 − 0.09
= 21 + 108 − 0.09
= 128.91 ≠ 68
Fourth option: ×, −, ÷, +
⇒ 21 × 3 − 36 ÷ 2 + 23 = 68
Solving the L.H.S. of the equation –
= 21 × 3 − 18 + 23
= 63 − 18 + 23
= 68

So, only the fourth option satisfies the given equation. Hence, the fourth option is correct.