Use the equation to answer the question.

Question

21H+ 21H→ 42H+energy

Which statement best describes the mass numbers of the atoms in the reaction?

(1 point)
Responses

There is one atom with a mass number of 1.
There is one atom with a mass number of 1.

There is one atom with a mass number of 2.
There is one atom with a mass number of 2.

There are two atoms with mass numbers of 1.
There are two atoms with mass numbers of 1.

There are two atoms with mass numbers of 2.

Answer 1

To analyze the equation:

\[ 21H + 21H \rightarrow 42H + \text{energy} \]

The notation \( 21H \) refers to hydrogen with a mass number of 2 (which indicates it is deuterium, an isotope of hydrogen). Thus, each \( 21H \) has a mass number of 2.

When two \( 21H \) (deuterium) atoms combine, they produce one \( 42H \) (which indicates a mass number of 4, as it represents an isotope of hydrogen called tritium).

Now let's evaluate the statements:

1. There is one atom with a mass number of 1. - Incorrect, there are no mass numbers of 1 in this equation.

2. There is one atom with a mass number of 2. - Incorrect, there are two atoms with a mass number of 2 before the reaction occurs, but none after.

3. There are two atoms with mass numbers of 1. - Incorrect, as there are no mass numbers of 1 in this equation.

4. There are two atoms with mass numbers of 2. - Correct, as you have two \( 21H \) atoms (each with mass number 2) before the reaction.

Based on the equation, the best choice is:

There are two atoms with mass numbers of 2.