Question

what is the missing particle?

190/78 pt→4/2 he+?

186/76 pt 186/76 os 194/80 hg

Explanation:

Step1: Calculate the mass number of the missing particle

The mass number of the reactant \(^{190}_{78}\text{Pt}\) is \(190\), and the mass number of the product \(\ce{^{4}_{2}He}\) is \(4\). Let the mass number of the missing particle be \(A\). According to the conservation of mass number in nuclear reactions \(A + 4=190\), so \(A = 190 - 4=186\).

Step2: Calculate the atomic number of the missing particle

The atomic number of the reactant \(^{190}_{78}\text{Pt}\) is \(78\), and the atomic number of the product \(\ce{^{4}_{2}He}\) is \(2\). Let the atomic number of the missing particle be \(Z\). According to the conservation of atomic number in nuclear reactions \(Z+2 = 78\), so \(Z=78 - 2 = 76\).

Step3: Determine the element corresponding to the atomic number

Looking at the periodic table, the element with atomic number \(Z = 76\) is Osmium (\(\text{Os}\)).

Answer:

\(\ce{^{186}_{76}Os}\)