At equilibrium,
a. all reactions have ceased.
b. only the forward reaction continues.
c. only the reverse reaction continues.
d. both the forward and reverse reactions continue.

d. both the forward and reverse reactions continue.


Equilibrium is when buyers will purchase exactly as much as sellers are willing to sell, what is the condition that has been reached
A market index is a resulting value created from the combination of several stocks and other  investment vehicles presenting its total value against a base value at a certain period. It is used to show the whole stock market at the same time keeping track with the way the market changes overtime. The practice of tracking the value of the stock market over a period of time can be used to benchmark to make a credible comparison of stock returns.

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