What does the half-life tell about a radioisotope? a. how long it takes for half of a sample to decay to another form b. how long it takes for half of the sample to begin to decay c. how long it takes a sample to lose half of its neutrons d. how long it takes a sample to become completely stable

It's option A as half life can be called as the time required for a radioisotope to decay into a more stable isotope compared to its current state.

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