Identify the number of neutrons present in a pair of element with atomic numbers 20 and 13 , if their mass numbers are 40 and 27 respectively.

Options

A. 20 and 13
B. 20 and 20
C. 17 and 20
D. 20 and 14

Explanation

To find the number of neutrons in the given elements, we can use the formula:

**Number of Neutrons = Mass Number - Atomic Number**

Let's solve for each element step by step.

### Step 1: Identify the first element
- **Atomic Number (Z)**: 20
- **Mass Number (A)**: 40

### Step 2: Calculate the number of neutrons for the first element
Using the formula:
\[ \text{Number of Neutrons} = A - Z \]
\[ \text{Number of Neutrons} = 40 - 20 \]
\[ \text{Number of Neutrons} = 20 \]

### Step 3: Identify the second element
- **Atomic Number (Z)**: 13
- **Mass Number (A)**: 27

### Step 4: Calculate the number of neutrons for the second element
Using the same formula:
\[ \text{Number of Neutrons} = A - Z \]
\[ \text{Number of Neutrons} = 27 - 13 \]
\[ \text{Number of Neutrons} = 14 \]

### Final Answer:
The number of neutrons in the first element (atomic number 20) is **20** and in the second element (atomic number 13) is **14**.

### Summary:
- For the element with atomic number 20 and mass number 40: **20 neutrons**
- For the element with atomic number 13 and mass number 27: **14 neutrons**

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