Atoms are the basic building blocks of matter. They consist of a nucleus, which contains protons and neutrons, surrounded by electrons. These subatomic particles carry electric charge, and the overall charge of an atom depends on the balance between the number of protons and electrons.

Charge of Protons:
- Protons are positively charged particles found in the nucleus of an atom.
- Each proton carries a charge of +1 elementary charge.

Charge of Electrons:
- Electrons are negatively charged particles that orbit around the nucleus.
- Each electron carries a charge of -1 elementary charge.

Neutral Atom:
- In a neutral atom, the number of protons is equal to the number of electrons.
- The positive charge of the protons is balanced by the negative charge of the electrons, resulting in a net charge of zero.

Explanation of the Options:

a) Positively charged:
- Atoms can become positively charged if they lose electrons.
- This process is called ionization.
- However, not all atoms are positively charged. Only atoms that have lost electrons can be positively charged.

b) Negatively charged:
- Atoms can become negatively charged if they gain electrons.
- This process is also called ionization.
- However, not all atoms are negatively charged. Only atoms that have gained electrons can be negatively charged.

c) Positively or negatively charged:
- This option is incorrect because atoms are not both positively and negatively charged at the same time.
- An atom can either be positively charged or negatively charged, depending on whether it has gained or lost electrons.

d) Not charged:
- This is the correct answer because the majority of atoms are neutral and do not carry a net charge.
- The number of protons in the nucleus is equal to the number of electrons orbiting around it, resulting in a balanced charge.

Conclusion:
- In summary, atoms are not charged in their neutral state.
- They can acquire a positive charge by losing electrons or a negative charge by gaining electrons.
- However, the majority of atoms exist in a neutral state, with no overall charge.

D