Question

Consider the following metals: Li, Na, K, Cu, Mg and Ag. The metals with the lowest and highest work function are respectively

• A. Na and Cu
• B. K and Cu
• C. Li and Ag
• D. Mg and Cu

Hint:

Think of the Reactivity Series: Caesium and Potassium are extremely reactive because they lose electrons easily (low work function). Copper and Platinum are noble because they hold onto their electrons (high work function).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The work function is the minimum energy required to remove an electron from the surface of a metal.
Metals with low ionization enthalpy (like alkali metals) have low work functions.
Step 2: Key Formula or Approach:
Work function depends on the electropositivity of the metal. Generally, as we move down a group (like Li to Cs), the work function decreases. Transition metals usually have higher work functions than s-block metals.
Step 3: Detailed Explanation:
Among the given list (Li, Na, K, Cu, Mg, Ag):
1. Alkali metals (Li, Na, K) have the lowest work functions because they easily lose valence electrons. Among them, Potassium (K) is the most electropositive and has the largest radius, hence the lowest work function.
2. Transition metals like Copper (Cu) and Silver (Ag) have significantly higher work functions. Between them, Copper (Cu) typically represents one of the higher values in this comparative set.
Therefore, K has the lowest and Cu has the highest work function in this context.
Step 4: Final Answer:
The metals are K and Cu.