Step 1: Reactivity Series Comprehension A metal's ability to displace hydrogen from acids is determined by its placement in the electrochemical series. Highly electropositive metals will react with acids to produce H$_2$ gas. Step 2: Metal Analysis Zn and Mn exhibit high reactivity and react readily with acids. Ni demonstrates moderate reactivity. Cu is positioned below hydrogen in the reactivity series, indicating it will not react with acids to liberate H$_2$. Conclusion: Copper (Cu) exhibits the lowest tendency to displace H$_2$ from acids.