Answer:
1. Mass of New atom = 208
2. Atomic number of the new atom is 82
3. Symbol of the new atom is Pb
Explanation:
²¹²₈₄Po —> ⁴₂He + ᴬZX
1. Determination of the mass A of the new atom.
212 = 4 + A
Collect like terms
212 – 4 = A
208 = A
A = 208
Therefore, the mass of the new atom is 208
2. Determination of the atomic number of the new atom.
84 = 2 + Z
Collect like terms
84 – 2 = Z
82 = Z
Z = 82
Therefore, the atomic number of the new atom is 82
3. Determination of symbol of the new atom
The atomic number of the new atom is 82. Comparing the atomic number of the new atom (i.e 82) with those in the periodic table, the new atom is Lead.
Lead has a symbol of Pb
Thus,
Mass of new atom (A) = 208
Atomic number of new atom (Z) = 82
Symbol of new atom (X) = Pb
Therefore,
ᴬZX = ²⁰⁸₈₂Pb
Answer: A) 3.21 g
Explanation:
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side.

We are given:
Mass of iron = 5.58 g
Mass of iron sulphide = 8.79 g
Mass of sulphur = x g
Total mass on reactant side = 5.58 + x
Total mass on product side = 8.79 g
Applying law of conservation of mass, we get:
Hence, the mass of reacting sulfur is 3.21 g.