Explanation:

Let's analyze the problem:

- We need the unit digit of 17¹²³.

- Only the unit digit of base (here, 7 from 17) affects the unit digit of its powers.

- The pattern of the unit digit of 7's powers is:

- 7¹ = 7

- 7² = 49 (9)

- 7³ = 343 (3)

- 7⁴ = 2401 (1)

- Then it repeats every 4.

- 123 ÷ 4 = 30 remainder 3.

- So, we look at the 3rd number in the pattern: 3.

Option:1 - 1 ?

Option:2 - 3

Option:3 - 7 ?

Option:4 - 9 ?

Correct Answer: Option:2, 3