When balancing a chemical equation, subscripts cannot be changed (option A), coefficients can be changed (option B), and the number of atoms can be changed by adjusting coefficients (option C). The correct statement is D: Subscripts and coefficients can both be changed.
When balancing a chemical equation, option D is true: both subscripts and coefficients can be changed. Balancing an equation involves ensuring that the number of atoms for each element on the reactant side is equal to the number of atoms on the product side, adhering to the law of conservation of mass.
Subscripts represent the number of atoms of each element within a molecule. In a chemical equation, changing subscripts is not allowed because it alters the identity of the compound. Subscripts define the molecular structure, and modifying them would result in a different chemical species.
On the other hand, coefficients are placed in front of chemical formulas to indicate the number of moles of each substance. Adjusting coefficients is a valid and necessary step in balancing the equation. Changing coefficients allows for the conservation of mass, ensuring that the total number of atoms for each element is the same on both sides of the arrow.
So, while subscripts remain fixed to maintain the chemical identity of the substances involved, coefficients are variable and can be adjusted to achieve a balanced chemical equation.