In what ph range do most biochemical reaction occur

The pH of blood is slighly basic (pH = 7.35).

So most of the biochemical reactions occurs in the pH range of 6.0 to 8.0. 

If the pH of solution largely different than 7.35, then the enzyme, which catalysis the biochemical reactions, will get denatured. Due to this, enzyme loses it's catalytic activity. 

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