On the basis of position in the electrochemical series, the metal which does not displace hydrogen from water and acid is

Hg

The correct answer is option 1. Hg.

To determine which metal does not displace hydrogen from water or acid based on its position in the electrochemical series, we need to consider the reactivity of metals with water and acids. Metals higher in the electrochemical series can displace hydrogen from water and acids, while those lower in the series typically cannot. Let us analyze each option:

1. Hg (Mercury):

Position in the electrochemical series: Hg is below hydrogen (H₂) in the electrochemical series. Reactivity with water and acids: Mercury (Hg) is not reactive enough to displace hydrogen from water or acids under normal conditions. It remains in its elemental form rather than forming ions that could react with water or acids.

2. Al (Aluminum):

Position in the electrochemical series: Al is above hydrogen (H₂) in the electrochemical series. Reactivity with water and acids: Aluminum (Al) is reactive enough to displace hydrogen from water and acids. It reacts with acids to liberate hydrogen gas and also reacts with water to produce aluminum hydroxide and hydrogen gas.

3. Pb (Lead):

Position in the electrochemical series: Pb is below hydrogen (H₂) in the electrochemical series. Reactivity with water and acids: Lead (Pb) is not reactive enough to displace hydrogen from water or acids. It typically forms insoluble compounds or remains as metallic lead without displacing hydrogen.

4. Ba (Barium):

Position in the electrochemical series: Ba is above hydrogen (H₂) in the electrochemical series. Reactivity with water and acids: Barium (Ba) is very reactive with water, and less so with acids, displacing hydrogen and forming barium hydroxide and hydrogen gas in water. In acids, barium typically displaces hydrogen gas.

Conclusion:

Based on their positions in the electrochemical series and their reactivity with water and acids, the metal that does not displace hydrogen from water and acid is: (1) Hg (Mercury).

Mercury is the correct answer because it is below hydrogen in the electrochemical series and is not reactive enough to displace hydrogen from water or acids. Therefore, mercury remains as elemental mercury rather than forming compounds with hydrogen from these substances.