An acid is a compound which will give H+ ions or H3O^+ ions
the reaction will be
![[Mn(H_{2}O )_{6} ^{+3} +H_{2}O --> [MnOH(H_{2}O)_{5}]^{+2} + H_{3}O^{+}](https://tex.z-dn.net/?f=%5BMn%28H_%7B2%7DO%20%29_%7B6%7D%20%5E%7B%2B3%7D%20%2BH_%7B2%7DO%20--%3E%20%5BMnOH%28H_%7B2%7DO%29_%7B5%7D%5D%5E%7B%2B2%7D%20%2B%20H_%7B3%7DO%5E%7B%2B%7D)
Thus as there is evolution of H_{3}O^{+} the Mn+3 is an acid
Nails are made up of iron not of phosphorus and barium.
As both phosphorous and barium are relatively weaker than iron ,phosphorus breaks easily and barium is also fairly weak. Iron nails are already also not that strong, but their weight and strength are sufficient.
So the nails are made up of iron.