Let's break down each of these concepts relating to the structure and properties of an atom:
a) An Atom in Neutral
An atom is considered neutral when it has an equal number of protons and electrons. Protons are positively charged particles found in the nucleus (the central part of the atom), whereas electrons are negatively charged particles that orbit the nucleus. Since the positive charge of protons and the negative charge of electrons cancel each other out, a neutral atom has an overall charge of zero. For example, a carbon atom has 6 protons and 6 electrons, making it neutral.
b) The Nucleus is Positively Charged
The nucleus of an atom is composed of protons and neutrons. Protons carry a positive charge, while neutrons have no charge (they are neutral). Because the protons contribute the positive charge, the nucleus itself is positively charged. This positive charge plays a significant role in the structure and behavior of the atom, as it attracts the negatively charged electrons that surround the nucleus, helping to keep them in orbit around it. For instance, in a helium atom, the nucleus contains 2 protons (and 2 neutrons), giving it a positive charge of +2.
c) Nucleus is the Heavier Part of the Atom
The nucleus is the heaviest part of the atom primarily because it contains most of the atom's mass. While electrons contribute very little to the total mass of an atom due to their much smaller mass compared to protons and neutrons, the nucleus is composed of protons and neutrons, which have significantly greater mass. In fact, each proton and neutron has a mass roughly 1836 times that of an electron. Therefore, when considering the total mass of an atom, the nucleus accounts for the vast majority of it, making it the heaviest part. For example, a carbon atom (which has 6 protons and 6 neutrons) has a nucleus mass of about 12 atomic mass units (amu), while the electrons contribute only a tiny fraction of an amu to the total mass.
In summary, an atom is neutral when protons equal electrons, the nucleus is positively charged due to protons, and the nucleus contains most of the atom's mass, making it the heaviest part.