Question

what is the missing particle?

225 89 ac → 4 2 he + ?

223 87 ac

221 87 fr

225 87 fr

Explanation:

Step1: Determine the mass number

The mass number of the reactant is \(225\), and the mass number of \(\ce{^4_2He}\) is \(4\). So the mass number of the missing particle is \(225 - 4=221\).

Step2: Determine the atomic number

The atomic number of the reactant (\(\ce{Ac}\)) is \(89\), and the atomic number of \(\ce{^4_2He}\) is \(2\). So the atomic number of the missing particle is \(89 - 2 = 87\).

Step3: Identify the element

Looking at the periodic table, the element with atomic number \(87\) is \(Fr\) (Francium).

Answer:

\(\ce{^221_87Fr}\)