The correct option is C (1√2,1√2)
Let’s check the magnitude for all these vectors. Whichever vector has the magnitude 1, it will be a unit vector.
so a) (12,1√2), Magnitude = √(12)2+(1√2)2=√32≠1
b) (1√2,1). Magnitude = √(12)2+(1)2≠1
c) (1√2,1√2). Magnitude = √(1√2)2+(1√2)2=1
So it is a unit vector
d) (1, 1), Magnitude = √(1)2+(1)2=√2≠1
So only (c) is a unit vector.