Question

Acceleration is a vector quantity which indicates that it's value_

Answer 1

acceleration is also a vector, and for the same reason as velocity.
since velocity has a magnitude and direction, acceleration indicates how they both are changing. pick up any book on vector analysis to see more rigorous treatment.

but the question is poorly worded. the (misspelled) "its" has no clear antecedent.

Answer 2

Good, I was falling sideways.