Respuesta :

Explanation:

Given parameters:

   Isotope ;

           Si - 28

           ²⁸₁₄Si;

The specie undergoes an alpha decay; An alpha particle resembles a helium atom;

           ²⁸₁₄Si   →  ⁴₂He  +   ?

In nuclear reactions, the mass and atomic numbers are usually conserved;

   So let specie unknown be denote as X

          ᵃₙX;

           ²⁸₁₄Si   →  ⁴₂He  +   ᵃₙX

Sum of the mass number on the reactant side must equal to that on the product side;

         28  = 4 + a

         28 - 4  = a

               a  = 24  mass number of X;

   14  = 2 + n

   n = 14 - 2  = 12   atomic number of X;

 Now, the species X with an atomic number of 12 is magnesium

  Symbol is Mg

   Mass number   = 24