Alpha rays emitted from a radioactive substance are

Options

A. negatively charged particles
B. ionised hydrogen nuclei
C. doubly ionised helium atom
D. uncharged particles having the mass equal to proton

Explanation

To solve the question regarding alpha rays emitted from a radioactive substance, we need to understand the nature of alpha rays and their characteristics. Here's a step-by-step breakdown:

### Step 1: Understand what alpha rays are
Alpha rays consist of alpha particles, which are made up of 2 protons and 2 neutrons. This means that they are essentially helium nuclei.

**Hint:** Remember that alpha particles are the same as helium nuclei.

### Step 2: Identify the process of alpha decay
When a radioactive substance undergoes alpha decay, it emits an alpha particle. This process results in a decrease in the atomic number of the original element by 2 and a decrease in the mass number by 4.

**Hint:** Focus on how the atomic number and mass number change during alpha decay.

### Step 3: Example of alpha decay
Consider the example of Polonium-240 (with atomic number 94). When it undergoes alpha decay, it transforms into Uranium-236 (with atomic number 92). The emitted alpha particle can be represented as \( ^4_2He \).

**Hint:** Use specific examples to visualize how alpha decay occurs and what particles are emitted.

### Step 4: Determine the identity of the emitted particle
Since an alpha particle consists of 2 protons and 2 neutrons, it can also be described as an ionized helium atom (He). This is important because it helps us identify the nature of the emitted alpha rays.

**Hint:** Remember that the emitted alpha particle is a helium nucleus, which is ionized.

### Step 5: Conclusion
Based on the characteristics of alpha rays and the example provided, we conclude that the correct description of alpha rays emitted from a radioactive substance is that they are ionized helium atoms.

**Final Answer:** Alpha rays emitted from a radioactive substance are ionized helium atoms.