Hint: Follow the law of mass conservation.
Explanation:

(1) According to Dalton’s atomic theory, atoms of different elements can join together in fixed, whole number ratios to produce a compound element. Also, the atoms of the same element can join with each other in a different, fixed ratio to form different elements.

This statement describes the law of chemical combination: the law of definite proportion and the law of multiple proportions. 

(2) The law of multiple proportions states that when two elements join together to form two or more compounds, the ratios of the masses of one element, which joins with the fixed mass of the other elements, are simple whole numbers.

(3) The law of definite proportions states that a chemical compound always consists of the same elements, combines together in the same proportion by mass.
 

(4) The law of conservation of mass is simply the law of  destructibility of matter during physical or chemical changes.

(5) Avogadro's law states that equal volumes of different gases contain the same number of molecules under similar conditions of temperature and pressure.

So, Avogadro's law and the law of conservation of mass are not related to the given statement.

Hence, option 1 is the correct answer.