Final answer:
When a mixture of oxygen and hydrogen is ignited, the total mass of the contents of the test tube remains the same.
Step-by-step explanation:
When a mixture of oxygen and hydrogen is ignited in a test tube, a chemical reaction occurs where water is formed. The reaction can be represented by the equation: 2H2 + O2 → 2H2O.
In this reaction, the total mass of the contents of the test tube remains the same before and after the reaction. According to the law of conservation of mass, matter cannot be created or destroyed, only rearranged.
Therefore, the total mass of the reactants (oxygen and hydrogen) is equal to the total mass of the products (water). It is important to note that the mass of each individual atom may change during the reaction, but the total mass remains constant.