Why is nitrobenzoic acid more acidic than ethanoic acid​

Explanation:

acidic strength increases if there is less electron density on a particular compound. and, as we know, greater the electron density on the compound,lesser acidic it will be.

Using activity series of metals (search topic), elements at top of series will replace any metal element below it but elements low on the series will not replace elements above. See reactions in explanation.

Explanation:

Pb(NO₃)₂(aq) + Mg(s) => Mg(NO₃)₂(aq) + Pb(s)

Cu(NO₃)₂(aq) + Mg(s) => Mg(NO₃)₂(aq) + Cu(s)

Fe(NO₃)₂(aq) + Mg(s) => Mg(NO₃)₂(aq) + Fe(s)

Cu(NO₃)₂(aq) + Pb(s) => Pb(NO₃)₂(aq) + Cu(s)

Fe(NO₃)₂(aq) + Pb(s) => No Reaction (Pb will not replace Fe according to the activity series of metals).