Hydrogen and oxygen present in a 1 to 2 ratio is water (H₂O).

Here's why:

* Hydrogen (H) has a valency of +1, meaning it can form one chemical bond.

* Oxygen (O) has a valency of -2, meaning it can form two chemical bonds.

To balance the charges and create a stable compound, you need two hydrogen atoms (2 x +1 = +2) to bond with one oxygen atom (-2). This results in the chemical formula H₂O.