Which among the following is a positively charged particle emitted by a radioactive element? A. Beta ray B. Alpha ray C. Cathode ray D. Gamma ray

The answer is $\boxed{\text{A}}$. A beta ray is a high-energy electron or positron emitted by an atomic nucleus during radioactive decay. It is a type of ionizing radiation.

Alpha rays are helium nuclei emitted by some radioactive nuclei. They are relatively heavy and slow-moving, and can be stopped by a sheet of paper.

Cathode rays are streams of electrons emitted from the cathode of a vacuum tube. They are used in cathode ray tubes (CRTs), which are found in televisions and computer monitors.

Gamma rays are high-energy photons emitted by radioactive nuclei. They are very penetrating and can be stopped only by thick layers of lead or concrete.