3 and 4 because the other two answers are different species.
The question is incomplete, here is the complete question:
Silicon reacts with carbon dioxide to form silicon carbide and silicon dioxide. Write the balanced chemical equation.
<u>Answer:</u> The balanced chemical equation is written below.
<u>Explanation:</u>
Every balanced chemical equation follows law of conservation of mass.
A balanced chemical equation is defined as the equation in which total number of individual atoms on the reactant side is equal to the total number of individual atoms on product side.
The balanced chemical equation for the reaction of silicon and carbon dioxide follows:

By Stoichiometry of the reaction:
2 moles of silicon reacts with 1 mole of carbon dioxide gas to produce 1 mole of silicon carbide and 1 mole of silicon dioxide
Hence, the balanced chemical equation is written above.
Moles of X are 0.925 moles.
A mole is a totally vital unit of dimension that chemists use.The mole, symbol mol, is the unit of amount of substance inside the worldwide device of gadgets. the amount quantity of the substance is a measure of how many simple entities of a given substance are in an item or sample. The mole is described as containing exactly 6.02214076×10²³ primary entities
mass of X2O3 = 4 g
so moles = mass/molar mass
molar mass of X2O3 = 2*X + 48 -
Given, that the mass of X = 2.8g
mass of O = 4 - 2.8 = 1.2g
A mole of O = 1.2g/16 = 0.075 mole
∴ mole of X = 1 - 0.075 = 0.925 moles.
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It is measured with a barometer