Loop2(n)
p <-- 1
for i <-- 1 to 2n do
p <-- p*i
Variable used in for loop is i. variable modify after each iteration is p actually. i remain unchange.
So for loop will run n time and complexity will be O(n).

@Arjun why it is assumed here that multiplication will take constant time? In general, do we need to consider constant TC for multiplication?, i don't think so.