Which of the following is not the property of β^- ray?

The correct answer is Option (3) → It is made of positively charged particles.

A \( \beta^{-} \) ray is a stream of fast electrons emitted from the nucleus when a neutron changes into a proton. Each particle carries the charge \( -e \) and has a very small mass.

Option (1) The ionising power is less than that of \( \alpha \)-particles. — A property of \( \beta^{-} \) rays. Light, fast electrons produce fewer ions per unit path than the heavy, doubly charged \( \alpha \)-particles.

Option (2) The penetrating power is greater than that of \( \alpha \)-particles. — A property of \( \beta^{-} \) rays. For the same reason they lose energy slowly and travel much farther through matter than \( \alpha \)-particles.

Option (3) It is made of positively charged particles. — Not a property of \( \beta^{-} \) rays (the answer). The particles of a \( \beta^{-} \) ray are electrons, which are negatively charged. Positively charged particles of this mass are positrons, emitted in \( \beta^{+} \) decay.

Option (4) It is deflected by an electric as well as by a magnetic field. — A property of \( \beta^{-} \) rays. They are charged, so an electric field and a magnetic field both deflect them.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Beta Decay – “… In beta-minus decay, a neutron transforms into a proton within the nucleus according to

    \( \displaystyle n \rightarrow p + e^{-} + \bar{\nu} \qquad (13.24) \)

whereas in beta-plus decay, a proton transforms into neutron (inside the nucleus) via

    \( \displaystyle p \rightarrow n + e^{+} + \nu \qquad (13.25) \)”