magnesium is a highly flammable element which is easily combustible in the presence of oxygen: 2mg + o2  --> ? ? + heatwhat is the unknown productmgob)mgo2c)2mgod)mg2o2

Answer is: C) 2MgO.

Balanced chemical reaction:  

2Mg + O₂ → 2MgO + heat.  

1) The same number of atoms is on each side of the equation: two magnesium atoms and two oxygen atoms.

2) In magnesium oxide (MgO), magnesium has oxidation number +2 and oxygen -2, because compound must be neutral.

3) The same mass is represented on each side of the equation: because there is same number of atoms, the mass is the same.