Alpha rays are not a part of the electromagnetic spectrum because alp…

The correct answer is Option (1) → consist of positively charged helium nuclei

Every member of the electromagnetic spectrum, from radio waves to gamma rays, is an electromagnetic wave. Such a wave is a self-sustaining oscillation of electric and magnetic fields that travels through vacuum. Radiation belongs to the spectrum because of this nature, whatever its wavelength.

Option (1) consist of positively charged helium nuclei — Correct. Alpha rays are a stream of material particles, each a helium nucleus with a charge of \( +2e \) and the mass of a helium atom. They are not oscillating electric and magnetic fields, so they have no place in the spectrum.

Option (2) are emitted by radioactive nuclei — Incorrect. Gamma rays are also emitted by radioactive nuclei, and they are electromagnetic waves. Coming from the nucleus does not decide whether a radiation belongs to the spectrum.

Option (3) carry energy from one place to another — Incorrect. Electromagnetic waves carry energy too, as light carries energy from the sun to the earth. A property shared by both cannot be the reason that separates them.

Option (4) cannot travel through vacuum — Incorrect. A beam of alpha particles moves through vacuum like any other moving charged particle. Electromagnetic waves also travel through vacuum, so this is not a difference between them.

NCERT (2026-27):
Nature of Electromagnetic Waves – “… We here make remarks on some features of electromagnetic waves. They are self-sustaining oscillations of electric and magnetic fields in free space, or vacuum. They differ from all the other waves we have studied so far, in respect that no material medium is involved in the vibrations of the electric and magnetic fields.”

Alpha-particle Scattering and Rutherford’s Nuclear Model of Atom – “… Alpha-particles are nuclei of helium atoms and, therefore, carry two units, 2e, of positive charge and have the mass of the helium atom. …”