Answer: Valence electrons
Valence electrons are those that are in the outermost or superficial layer of the atom, which means they have the highest energy compared to those of the inner layers.
Because of their position, it is easier for these electrons to interact with other atoms of their own element as well as different elements. This is done through the process of forming bonds when being attracted by other atoms.
Gap junctions in the intercalated discs allow impulses to be spread across the heart more quickly. This is because gap junctions allow particles/signals to pass through, thus making cells with gap junctions more able to interact.
One more thing—you posted this in the physics section rather than biology.
Option A, current (thumb) to magnetic field (fingers)
As per the First right-hand rule,
Using right hand, if we suppose that thumb points towards the electric current
fingers curl towards the magnetic field
