27/13AL+? ->> 24/11NA+4/2HE

 ¹₀n

Explanation:

The given expression is:

          ²⁷₁₃Al      +     ₐᵇT   →   ²⁴₁₁Na    +    ⁴₂He

This expression is typical of nuclear reactions. To balance this expression we must conserved the mass number and the atomic number.

The mass number is the superscripts and the atomic number is the subscript;

 Now;

 conserving mass number:

             27 + b  = 24 + 4

             27 + b  = 28  

                   b  = 28 - 27  = 1

conserving the atomic number;

            13 + a  = 11 + 2

             13 + a  = 13

                    a  = 0

So;

The particle T is a neutron    ¹₀n