Explanation

This tests cyclicity of last digits. Powers of 17 end in 7, 9, 3, 1 repeating with period 4 (17¹→7, 17²→9, 17³→3, 17⁴→1). Since 256 is divisible by 4, 17²⁵⁶ completes the cycle and ends in 1. Option (b) 7 is the trap from using the first power's digit. Hence option (d).