The value of A in the following reaction is: 4 Be9 + 2He4 = 6CA + on1

Explanation

On the left-hand side of the reaction, we have the sum of the mass numbers of the reactants: Mass number before the reaction = 9 (mass number of 4Be9) + 4 (mass number of 2He4) = 13. On the right-hand side of the reaction, we have the sum of the mass numbers of the products: The mass number after the reaction = A (mass number of 6CA) + 1 (mass number of 0n1). Since the reaction involves a neutron as one of the products, its mass number is 1. Therefore, the mass number after the reaction is A + 1. Now, equating the mass numbers before and after the reaction: 13 (mass number before the reaction) = A + 1 (mass number after the reaction). To find the value of A, we can rearrange the equation: A = 13 - 1 = 12. So, the value of A for the unknown isotope ^6_C A is 12.