Question

Assertion: On burning magnesium in oxygen the mass of magnesium oxide formed is equal to the
total mass of magnesium and oxygen
reason in a chemical substance the elements are always present in a definite proportion
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Answer 1

Answer:

When the magnesium metal burns it reacts with oxygen found in the air to form Magnesium Oxide. A compound is a material in which atoms of different elements are bonded to one another. Oxygen and magnesium combine in a chemical reaction to form this compound. After it burns, it forms a white powder of the magnesium oxide. Magnesium gives up two electrons to oxygen atoms to form this powdery product. This is an exothermic reaction as well as combination reaction.

2Mg(s)+O 2(g)→2MgO(s)+energy

Answer 2

both A and R correct but R is not the correct explanation of this is given by rule mass can neither be created nor destroyed in a chemical reaction.

The equation is: Magnesium + oxygen → magnesium oxide. 2Mg + O2 → 2MgO.