(N/A) Two vectors are said to be equal if they have the same magnitude and the same direction.
$1$. Vector $\vec{a}$ has a magnitude of $1 \text{ unit}$ and points in a specific direction.
$2$. Vector $\vec{b}$ has a magnitude of $2 \text{ units}$ and points in a different direction.
$3$. Vector $\vec{c}$ has a magnitude of $1 \text{ unit}$ and points in the same direction as $\vec{a}$.
$4$. Vector $\vec{d}$ has a magnitude of $2 \text{ units}$ and points in the opposite direction to $\vec{b}$.
Comparing these,vectors $\vec{a}$ and $\vec{c}$ have the same magnitude $(1 \text{ unit})$ and the same direction.
Therefore,the equal vectors are $\vec{a}$ and $\vec{c}$.