**Core Concept**
Radioactive isotopes or substances emit various forms of ionizing radiation due to the instability of their atomic nuclei. These emissions can be categorized into alpha, beta, and gamma radiation.

**Why the Correct Answer is Right**
The type of radiation emitted depends on the mode of decay. Alpha decay involves the emission of an alpha particle (2 protons and 2 neutrons), which is a helium nucleus. Beta decay can occur in two forms: beta minus (β-) emission, where a neutron is converted to a proton and an electron, and beta plus (β+) emission, where a proton is converted to a neutron and a positron. Gamma radiation, on the other hand, is electromagnetic radiation of high energy and is emitted when a nucleus transitions to a lower energy state.

**Why Each Wrong Option is Incorrect**
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**Option B:** This option is blank. Please provide the options for the question.
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**Option D:** This option is blank. Please provide the options for the question.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the type of radiation emitted by a radioactive substance is crucial in determining the safety precautions required for handling it.

**Correct Answer:**