The number of moles of hydrogen that is needed to produce 0.253 mol of water is

2H₂ + O₂ = 2H₂O

n(H₂O)=0.253 mol

n(H₂)=n(H₂O)=0.253 mol

The number of moles of hydrogen that is needed to produce 0.253 mol of water is 0.253.

The activity series is shown in the attached picture. if the element is below the other, then you can displace the other. following the activity series as a guide, the reactions are as follows: nickel and aluminum chloride3 ni + 2 alcl₃  → 3 nicl₂ + 2 albarium and copper bromideba + cubr  →  no reaction because cu is less oxidizable than bapotassium nitrate and aluminum3 kno₃ + al  → al(no₃)₃ + 3 ksodium phosphate and zincnaso₄ + zn  → znso₄ + na