$0.4\hat i + 0.8\hat j + c\hat k$ represents a unit vector when $c$ is

If a unit vector is represented by $0.5\hat i + 0.8\hat j + c\hat k$,then the value of $c$ is

Distinguish between a vector quantity and a scalar quantity.

State whether the following statements are true or false:
$(a)$ The unit vectors ${\hat i}$ and ${\hat j}$ along the $x$ and $y$-axes change with time.
$(b)$ If the angle between $\overrightarrow A$ and $\overrightarrow B$ is ${\theta _1}$ and the angle between $\overrightarrow A$ and $\overrightarrow C$ is ${\theta _2}$,then $\overrightarrow A \cdot \overrightarrow B = \overrightarrow A \cdot \overrightarrow C$ implies $\overrightarrow B = \overrightarrow C$.
$(c)$ The resultant vector of two coplanar vectors is also a coplanar vector.

$A$ vector is added to an equal and opposite vector of similar nature,it forms a ........

If $\vec{A} + \vec{B} = \vec{C}$ and $|\vec{A}| = |\vec{B}| = |\vec{C}|$,then the angle between $\vec{A}$ and $\vec{B}$ is ....... $^o$.