Identify the coefficients and subscripts in each formula: H₂, 2 HCl, 4 O₂, CH₄, 3 CO₃, 2 NaOH

What you are looking for in each formula

You need to separate two kinds of numbers:

• Coefficient: a number written in front of the whole chemical formula, it multiplies the entire formula unit.
• Subscript: a small number written after an element symbol, it tells how many atoms of that element are in one formula unit.

Marking each item (coefficient, then subscripts)

• $H_2$: coefficient $1$; subscript $2$ applies to $H$.
• $2HCl$: coefficient $2$; no subscripts (so $H$ is 1 and $Cl$ is 1).
• $4O_2$: coefficient $4$; subscript $2$ applies to $O$.
• $CH_4$: coefficient $1$; subscript $4$ applies to $H$ (and $C$ has an implied 1).
• $3CO_3$: coefficient $3$; subscript $3$ applies to $O$ (and $C$ has an implied 1).
• $2NaOH$: coefficient $2$; no subscripts (so $Na$, $O$, and $H$ are each 1).

Quick check idea

If there is no number in front, the coefficient is assumed to be $1$. If an element has no subscript, its subscript is assumed to be $1$.