Skill: Add zero

Adding zero to a whole number leaves its value unchanged: $n+0=n$ and $0+n=n$, including numbers represented in ones, tens, and hundreds. This understanding distinguishes zero as the additive identity—not a quantity that makes the other addend zero—and supports accurate mental computation and equation reasoning within grade-appropriate whole-number ranges, without extending to negative numbers, fractions, or formal algebraic generalization.