Balance the redox reaction equation (occurring in acidic solution) and choose the correct coefficients for each reactant and (s)+__sn(s)+__h+(aq)→__pb2+(aq)+__s n2+(aq)+__h2o(l)

Balanced chemical reaction: 
PbO₂(s) + Sn(s)+ 4H⁺(aq) → Pb²⁺(aq) + Sn²⁺(aq) + 2H₂O(l).
Oxidation half-reaction: Sn → Sn²⁺ + 2e⁻.
Reduction half-reaction: PbO₂ + 4H⁺ + 2e⁻ → Pb²⁺ + 2H₂O.
Net reaction: Sn + PbO₂ + 4H⁺ + 2e⁻ → Sn²⁺ + 2e⁻ + Pb²⁺ + 2H₂O.
Oxidation is increase of oxidation number, reduction is decrease of oxidation number.

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts