A deuterium is

Options

A. an electron with a positive charge
B. a nucleus having two protons
C. a nucleus containing a neutron and two protons
D. a nucleus containing a neutron and a proton.

Explanation

To solve the question "A deuterium is," we need to understand the definition and characteristics of deuterium, which is an isotope of hydrogen. Here’s a step-by-step solution:

### Step 1: Understand the concept of isotopes
Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons. For hydrogen, there are three isotopes: protium (1 proton, 0 neutrons), deuterium (1 proton, 1 neutron), and tritium (1 proton, 2 neutrons).

**Hint:** Remember that isotopes differ in their neutron count while having the same number of protons.

### Step 2: Identify the composition of deuterium
Deuterium is specifically an isotope of hydrogen with:
- 1 proton (which is the atomic number, Z = 1)
- 1 neutron (which contributes to the mass number, A = 2)

This means that the mass number (A) of deuterium is 2 (1 proton + 1 neutron).

**Hint:** The mass number (A) is the total number of protons and neutrons in the nucleus.

### Step 3: Analyze the answer choices
Now, let’s evaluate the given options:
1. An electron with a positive charge - Incorrect, as deuterium is not an electron.
2. A nucleus having 2 protons - Incorrect, as deuterium has only 1 proton.
3. A nucleus containing a neutron and 2 protons - Incorrect, as deuterium has 1 neutron and 1 proton.
4. A nucleus containing 1 neutron and 1 proton - This is the correct definition of deuterium.

**Hint:** Carefully check each option against the known characteristics of deuterium.

### Conclusion
Based on the analysis, the correct answer is that deuterium is a nucleus containing 1 neutron and 1 proton.

**Final Answer:** A nucleus containing 1 neutron and 1 proton.