The correct option is D equal to its magnitude.
Let a vector be →A
We know that the projection of →Aalong →A is given as
→A⋅→A|→A|=|→A||→A|cosθ|→A|=|→A|cosθ
Since, the projection is on itself,
cosθ=cos0∘=1
⇒ |→A|cosθ=|→A|
Hence, projection of a vector onto itself is its magnitude.