CSS - PMS - CCE - PCS - General Science
Modern Physics - Atom
What determines the chemical element to which an atom belongs?
A. Number of protons
B. Number of neutrons only
C. Number of electron shells only
D. Atomic mass alone
Correct Answer: A
Atomic number, equal to proton count, defines the element.
CSS - PMS - CCE - PCS - General Science
Modern Physics - Atom
What is an ion?
A. An atom or molecule with a net electric charge
B. A photon
C. A molecule with no electrons or protons ever
D. A neutral neutron only
Correct Answer: A
Ions form when electrons are gained or lost.
CSS - PMS - CCE - PCS - General Science
Modern Physics - Atom
What experiment led Rutherford to propose a small dense nucleus?
A. Michelson-Morley experiment
B. Gold-foil scattering experiment
C. Millikan oil-drop experiment
D. Young's double-slit experiment
Correct Answer: B
Large-angle alpha scattering showed that positive charge and mass are concentrated in a tiny nucleus.
CSS - PMS - CCE - PCS - General Science
Modern Physics - Atom
Which model introduced quantized electron energy levels for hydrogen?
A. Fluid model
B. Bohr model
C. Plum pudding model only
D. Dalton solid-sphere model only
Correct Answer: B
Bohr proposed discrete electron orbits/energy levels for hydrogen.
CSS - PMS - CCE - PCS - General Science
Modern Physics - Atom
What particles are found in the atomic nucleus?
A. Electrons only
B. Ions only
C. Protons and neutrons
D. Photons only
Correct Answer: C
The nucleus is composed of nucleons: protons and neutrons.
CSS - PMS - CCE - PCS - General Science
Modern Physics - Atom
What is an atom?
A. A visible dust particle only
B. The smallest unit of an element that retains its chemical identity
C. A molecule made of many elements only
D. A proton with no electrons always
Correct Answer: B
Atoms contain nuclei and electrons and define chemical elements by proton number.