Import Question JSON

$\text{Let's analyze each statement:}$ $1.\ \text{The oxidation number of hydrogen is always } +1\text{.}$ $\text{This statement is incorrect.}$ $\text{While hydrogen's oxidation number is } +1 \text{ in most compounds (e.g., hydrogen halides, acids, and compounds with non-metals), it can also have an oxidation number of } -1 \text{ in metal hydrides (e.g., } \text{NaH}, \text{CaH}_2\text{).}$ $\text{In its elemental form } (\text{H}_2)\text{, the oxidation number of hydrogen is } 0\text{.}$ $2.\ \text{The algebraic sum of all the oxidation numbers carried by elements in a compound is zero.}$ $\text{This statement is correct.}$ $\text{For a neutral compound, the sum of the oxidation numbers of all atoms is zero.}$ $3.\ \text{An element in its free or uncombined state has an oxidation number of zero.}$ $\text{This statement is correct.}$ $\text{For example, the oxidation number of } \text{O} \text{ in } \text{O}_2 \text{, } \text{H} \text{ in } \text{H}_2 \text{, } \text{Cl} \text{ in } \text{Cl}_2 \text{, and } \text{Na} \text{ in solid sodium metal is } 0\text{.}$ $4.\ \text{Generally, in all its compounds, the oxidation number of fluorine is } -1\text{.}$ $\text{This statement is correct.}$ $\text{Fluorine is the most electronegative element in the periodic table. Due to its exceptionally high electronegativity, it always exhibits an oxidation state of } -1 \text{ in all its compounds.}$ $\text{Therefore, the incorrect statement is number 1.}$