how does the law of conservation of matter explain how you write nuclear equations

 The law of conservation of matter requires that no mass is lost in , as it is commonly stated matter can neither be created nor destroyed.

 In the case of a nuclear reaction it requires the total mass in the reactant side must be equal to the total mass in the product side , in other word that the mass on the left hand side must be equal to the mass on the right hand side and vice versa.

 The entails that the sum of the mass  numbers of all the participating atoms on the left hand side must be equal to the sum of the mass number of the all atoms on the product side, in other word the atoms on the atomic “masses” on the reactant side must be equal to the atomic “masses” on the product side.

Also the total atomic numbers of all the participating atoms on the reactant side must be equal to the total number of all the atomic number of all the atoms formed on the product side.

In other words the total nuclear charges on the left hand side must be equal the total nuclear charge in the right hand side.

 What the law requires from you is balance the atomic number and the atomic masses on both the two  sides.

 For example in the reaction below

²³⁴ ₉₀Th → ²³⁴ ₉₁Ac + ⁰ _-1e

 The total mass on the left hand side is 234 and also on the right hand side is 234+0 = 234, therefore everything is balanced

 Like the total charges in the left hand side is 90 and likely on the right hand side is 91+(-1) = 90

 Therefore everything is balanced.

  These did not abrogate the fact that masses are lost and energy is created in nuclear reaction. Becuae here we are dealing with mass number which are whole number and not the actual nuclei masses.