If a is a non-zero vector, then always

The correct answer is Option (2) → \(\vec{a}.\vec{a} \gt 0\)

The dot product of a vector with itself is the square of its magnitude (the angle between \(\vec{a}\) and itself is 0):

    \(\vec{a}\cdot\vec{a} = |\vec{a}||\vec{a}|\cos 0 = |\vec{a}|^2\)

Since \(\vec{a} \ne \vec{0}\), \(|\vec{a}| \gt 0\), so \(\vec{a}\cdot\vec{a} = |\vec{a}|^2 \gt 0\).

It equals 1 only when \(\vec{a}\) is a unit vector, so Option (4) is not always true.