The nucleon number of atom X is 37. It exists as a diatomic molecule, `X_2`. One molecule of `X_2` contains 34 protons. How many neutrons are present in the nucleus of atom X?

Options

A. 17
B. 20
C. 21
D. 25

Explanation

To solve the problem step by step, we will follow these logical steps:

### Step 1: Understand the given information
- The nucleon number (mass number) of atom X is 37.
- Atom X exists as a diatomic molecule, denoted as \(X_2\).
- One molecule of \(X_2\) contains 34 protons.

### Step 2: Determine the number of protons in one atom of X
Since \(X_2\) is a diatomic molecule, it consists of two atoms of X. Therefore, the number of protons in one molecule of \(X_2\) (which is 34) can be divided by 2 to find the number of protons in one atom of X.

\[ \text{Number of protons in one atom of X} = \frac{34}{2} = 17 \]

### Step 3: Identify the atomic number of atom X
The number of protons in an atom is equal to its atomic number. Therefore, the atomic number of atom X is 17.

### Step 4: Use the nucleon number to find the number of neutrons
The nucleon number (mass number) is the sum of the number of protons and neutrons in the nucleus. We can express this relationship as:

\[ \text{Nucleon number} = \text{Number of protons} + \text{Number of neutrons} \]

Given that the nucleon number of atom X is 37 and we have already found that the number of protons is 17, we can rearrange the equation to find the number of neutrons:

\[ \text{Number of neutrons} = \text{Nucleon number} - \text{Number of protons} \]

Substituting the known values:

\[ \text{Number of neutrons} = 37 - 17 = 20 \]

### Step 5: Conclusion
Thus, the number of neutrons present in the nucleus of atom X is 20.

### Final Answer:
The number of neutrons in the nucleus of atom X is **20**.

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