Answer:
Hence, All integers where n ≥ 1
Option 2 is correct. 
Explanation:
Given: The geometric sequence 
where, a1 = a = 5 and the common ratio (r) = −3
Now we will find the general term of Geometric sequence. 


Now we write as function, 

f(1)=5
For n=1, 
Geometric series start from n=1 
Therefore, Domain: n≥1
Hence, All integers where n ≥ 1