The principle of conservation of matter states that matter cannot be created or destroyed in a chemical reaction. This implies that the number of atoms of each element must be the same on both the reactants and products sides of the reaction.
Let's analyze the given options:
A. K + MgBr → KBr + Mg
- Reactants: 1 K, 1 Mg, 1 Br
- Products: 1 K, 1 Br, 1 Mg
- 1 K, 1 Mg, and 1 Br are conserved. This reaction upholds the principle.
B. K + 2MgBr → KBr + 2Mg
- Reactants: 1 K, 2 Mg, 2 Br
- Products: 1 K, 2 Mg, 1 Br
- 1 K is conserved, but 2 Br in reactants and 1 Br in products indicates a loss of matter.
C. 2K + MgBr → 2KBr + Mg
- Reactants: 2 K, 1 Mg, 1 Br
- Products: 2 K, 1 Br, 1 Mg
- 2 K, 1 Br, and 1 Mg are conserved. This reaction upholds the principle.
D. 2K + 2MgBr → KBr + 2Mg
- Reactants: 2 K, 2 Mg, 2 Br
- Products: 1 K, 2 Mg, 1 Br
- Not balanced; 2 K and 2 Br in reactants aren't matched in products.
Based on this analysis, both A and C uphold the principle of conservation of matter, but since only one option is needed:
A. K + MgBr → KBr + Mg is the best option that showcases stoichiometric balance, but C is equally valid.
If I must pick one, I would select: C. 2K + MgBr → 2KBr + Mg as it maintains the conservation of matter with a clear depiction of atom count on both sides.