When is the linear momentum of a body or system of bodies conserved?
Linear momentum is conserved when net force is zero,
Is electric current a scalar or a vector?
Electric current is a scalar quantity. It has both magnitude and direction but it does not obey the law of addition of vectors. It is simply added as a scalar quantity.
Is pressure a scalar or a vector quantity?
Pressure is a scalar quantity. Even though it contains force, which is a vector. But actually in the pressure definition, we take only the normal (or perpendicular) component of the force, that is only one component of force. So, it is a scalar quantity.