Answer:
a) electrons
b) from Y to X
Step-by-step explanation:
positive protons are the cores of atoms in relative to electrons very, very heavy.
the outer electrons of atoms can move, under certain conditions, away from the atom, leaving it electrically unbalanced -> positively charged
there can also be a surplus of electrons on many surfaces, leading to a static negative charge. you know this when you are charged and you discharge with an object or another person, electrically balancing the two bodies charge.
electrons are also much smaller. they are the "things" to move, let it be trough the air or trough a wire, while the heavy protons will stay in place (unless the materials is melted of course, extreme heat brakes the bounds between atoms relatively well)