The four metals that will not replace hydrogen in an acid are Cu, Ag, Au, Hg.
Explanation:
- As Copper Cu lies below the hydrogen, this is why it is less reactive and ca not replace Hydrogen from its compound.
- Silver Ag also lies below the hydrogen and therefore it is less reactive to displace Hydrogen.
- Gold Au becomes less reactive than Hydrogen due to its placement below Hydrogen acid.
- Mercury Hg is less reactive than Hydrogen
