Answer
The chemical formula for sodium hydroxide is : $NaOH$
Work Step by Step
** Since the last name is "hydroxide", we can assume that it will act as a base in water.
"Sodium" is the full name for the element: $Na$, which is from the group I of the periodic table. Therefore, its charge will be equal to $1+.$
"Hydroxide" represents the ion formed by a hydrogen and an oxygen atom, with a single negative charge: $OH^-$. (Hydroxide ion)
Since the charges are already balanced ("+1" and "-1"), we can simply put these 2 ions together:
$NaOH$