Final answer:
The statement that a reaction will not occur if the free element is below the element to be replaced in the activity series is true. The activity series ranks elements by reactivity, and only a more reactive element (one that is higher in the series) can replace a less reactive element in a compound during a single-replacement reaction.
Step-by-step explanation:
The statement 'In the activity series, if the free element is below the element to be replaced in the compound, then the reaction will not occur.' is true. The activity series is a list that ranks elements according to their chemical reactivity. The more reactive an element is, the more likely it is to replace a less reactive element in a compound, during a single-replacement reaction. For instance, if we have nickel and we place it in a solution of iron (III) nitrate, no reaction will occur because nickel is below iron in the activity series. Conversely, nickel can replace lead in a lead (II) nitrate solution, as it is above lead in the series. The general rule is that a metal can replace another metal that it precedes in the activity series.
For example:
- Ni (s) + Pb(NO3)2 (aq) → Ni(NO3)2 (aq) + Pb (s) (reaction occurs)
- Ni (s) + Fe(NO3)3 (aq) → NR (no reaction)
This principle assists in predicting whether a single-replacement reaction will take place or not.