Which sequence is correct regarding the first ionisation potential of coinage metals ?

Options

A. `Cu gt Ag lt Au`
B. `Cu gt Ag gt Au`
C. `Cu lt Ag lt Au`
D. `Au gt Ag lt Cu`

Explanation

To determine the correct sequence regarding the first ionization potential of coinage metals (copper, silver, and gold), we need to analyze the trends in ionization potential for these elements. Here's a step-by-step solution:

### Step 1: Identify the Coinage Metals
The coinage metals are:
- Copper (Cu)
- Silver (Ag)
- Gold (Au)

### Step 2: Understand the Electron Configuration
- Copper (Cu): [Ar] 3d^10 4s^1
- Silver (Ag): [Kr] 4d^10 5s^1
- Gold (Au): [Xe] 4f^14 5d^10 6s^1

### Step 3: Analyze the Trends in Ionization Potential
1. **From Copper to Silver**:
- As we move from copper to silver, the atomic size increases due to the addition of electron shells.
- Larger atomic size generally leads to a decrease in ionization potential because the outer electrons are further from the nucleus and experience less nuclear charge.

2. **From Silver to Gold**:
- When moving from silver to gold, we see that gold has a filled 4f subshell. The presence of the 4f electrons provides poor shielding for the outer 5s and 5d electrons.
- Although gold is lower in the periodic table, the effective nuclear charge felt by the outermost electrons increases due to the poor shielding effect of the 4f electrons. This results in a decrease in atomic size and an increase in ionization potential.

### Step 4: Establish the Order of Ionization Potential
Based on the analysis:
- The order of first ionization potential from highest to lowest is:
- **Copper (Cu) > Gold (Au) > Silver (Ag)**

### Conclusion
Thus, the correct sequence regarding the first ionization potential of coinage metals is:
- **Cu > Au > Ag**