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# If $\overrightarrow{a}$ is a non-zero vector and $m$ is a non-zero scalar then $m\overrightarrow{a}$ is a unit vector if

$\begin{array}{1 1} (1)m=\neq\pm 1 &(2)a=| m | \\ (3)a=\large\frac{1}{|m|}& (4)a=1\end{array}$

Given $\overrightarrow{a} \neq \overrightarrow{0}$ and $m$ is a scalar.
$|m \overrightarrow{a}|=1 => |m| | \overrightarrow{a}|=1$
=> $| \overrightarrow {a}| = \large\frac{1}{|m|}$
$a=\large\frac{1}{|m|}$
Hence 3 is the correct answer.