MCQs on Atomic Structure

What is the smallest part of an element that can take part in a chemical change?

• Molecule

• Atom

• Proton

• Neutron

Answer explanation

The smallest part of an element that can participate in a chemical change is an atom. Atoms are the basic building blocks of matter, while molecules are made of two or more atoms. Protons and neutrons are subatomic particles within an atom.

Which of the following particles has a negative charge?

• Proton

• Neutron

• Electron

• Nucleus

Answer explanation

The electron is the only particle listed that has a negative charge. Protons have a positive charge, neutrons are neutral, and the nucleus is made up of protons and neutrons, thus not carrying a charge itself.

The mass of a proton is approximately:

• 1 atomic mass unit (amu)

• 0 amu

• 1836 amu

• 1/1836 amu

Answer explanation

The mass of a proton is approximately 1 atomic mass unit (amu), which is a standard unit used to express atomic and molecular weights. The other options are incorrect as they do not accurately represent the mass of a proton.

What is the symbol for potassium?

• Po

• Pt

• K

• P

Answer explanation

The symbol for potassium is 'K', derived from its Latin name 'kalium'. The other options, 'Po', 'Pt', and 'P', represent polonium, platinum, and phosphorus, respectively, making 'K' the correct choice.

Which subatomic particle has no charge?

• Proton

• Electron

• Neutron

• Positron

Answer explanation

The neutron is a subatomic particle found in the nucleus of an atom and has no electric charge, making it neutral. In contrast, protons are positively charged, electrons are negatively charged, and positrons are the antimatter counterpart of electrons.

Where are electrons found in an atom?

• Inside the nucleus

• Orbiting the nucleus in shells

• Fixed in the center

• Randomly scattered throughout

Answer explanation

Electrons are found orbiting the nucleus in defined energy levels or shells. This arrangement allows them to maintain a stable distance from the nucleus, unlike being fixed in the center or randomly scattered.

The atomic number of an element is equal to:

• The number of neutrons

• The number of protons

• The number of electrons

• The number of nucleons

Answer explanation

The atomic number of an element is defined as the number of protons in its nucleus. This number determines the element's identity and its position in the periodic table, making 'the number of protons' the correct answer.

Which statement about isotopes is correct?

• They have different numbers of protons

• They have the same mass number

• They have the same number of neutrons

• They have the same number of protons but different numbers of neutrons

Answer explanation

Isotopes are variants of the same element that have the same number of protons (defining the element) but different numbers of neutrons, leading to different mass numbers. Thus, the correct statement is that they have the same number of protons but different numbers of neutrons.

The beam of electrons in a cathode-ray tube is deflected by:

• Gravitational fields only

• Magnetic and electric fields

• Heat energy

• Sound waves

Answer explanation

The beam of electrons in a cathode-ray tube is influenced by magnetic and electric fields, which can change the direction of the electrons. Gravitational fields, heat energy, and sound waves do not significantly affect the electron beam.

Which of the following is NOT a part of an atom?

• Proton

• Neutron

• Photon

• Electron

Answer explanation

A photon is not a part of an atom; it is a particle of light. In contrast, protons, neutrons, and electrons are the fundamental components that make up an atom.