Hydrogen gas (H2) and oxygen gas (O2) react to form liquid hydrogen peroxide (H2O2). Which statement is true about the reaction?
A.
The same atoms are present, so the chemical properties are the same.
B.
The atoms of the reactants have combined to form a new substance.
C.
The two gases have mixed together, but a new substance has not formed.
D.
The product that is formed has the same physical properties as the reactants.

B. The atoms of the reactants have combined to form a new substance.

Explanation:

When hydrogen and oxygen gas combined they form hydrogen peroxide. This is happen through chemical reaction so a new substance is formed. The state of reactant is also different, reactants are present in gaseous form while product is present in liquid form. So option b is correct.

Chemical change:

The changes, that occur due to change in the composition of a substance and result in a different compound is known as chemical change.

These changes are irreversible

These changes occur due to chemical reactions

These may not be observed with naked eye

Example:

Combustion of fuel or wood: that oil or wood convert into energy, CO2 and ash in case of wood

Boiling of egg: that change the chemical composition of protein in the egg .

The reaction of Hydrogen and oxygen:

H 2 (g)  + O 2  (g) > H2O2  (l)

Explanation: The chemical reaction has combined the atoms of hydrogen gas and the atoms of oxygen gas to form a new substance. Since hydrogen peroxide is a different substance, it has different chemical and physical properties. All chemical reactions produce new substances with different chemical and physical properties than the reactants.