The least positive integer value of n, if $$\left( \frac{1 + i}{1 - i} \right)^{n} = 1$$​ is:

Correct option is D

Given:
​$$\left( \frac{1 + i}{1 - i} \right)^{n} = 1$$​​
Formula used:
$$i^{n} = 1 \Rightarrow n$$​ is a multiple of 4
Also,
​$$\frac{1 + i}{1 - i} = \frac{(1 + i)^{2}}{1^{2} + 1^{2}}$$​​
Solution:
​$$\frac{1 + i}{1 - i}= \frac{(1 + i)(1 + i)}{(1 - i)(1 + i)}= \frac{1 + 2i + i^{2}}{1 - i^{2}}= \frac{2i}{2}= i$$​​
So the given equation becomes:
​$$i^{n} = 1$$​​
The least positive integer n for which $$i^{n} = 1$$​ is:
n = 4
The correct answer is (d) 4.