Which one of the following statements about lanthaniodesis false ?

Options

A. Lanthanides are sepearated from one another by ion exchange method
B. The ionic radii of trivalent lanthanides steadily increases with increases in atomic number
C. All lanthanides are highly dense metals
D. Most typical oxidation state of lanthanides is +3

Explanation

To determine which statement about lanthanoids is false, let's analyze each statement step by step.

### Step 1: Understand the Electronic Configuration of Lanthanoids
Lanthanoids have a general electronic configuration of \[ (n-2)f^{14} (n-1)s^2 (n-1)p^6 (n)d^{1-10} ns^2 \]. This means they have filled 4f orbitals and two electrons in the outermost s orbital.

**Hint:** Remember the general electronic configuration of lanthanoids to understand their properties.

### Step 2: Evaluate the First Statement
**Statement 1:** "Lanthanoids are separated from one another by ion exchange method."
This statement is true. Lanthanoids are chemically similar due to their similar ionic radii, making them difficult to separate. Ion exchange methods are commonly used for their separation.

**Hint:** Consider the similarities in ionic radii when thinking about separation methods.

### Step 3: Evaluate the Second Statement
**Statement 2:** "The ionic radii of trivalent lanthanoids steadily increases with the increase in atomic number."
This statement is false. The ionic radii of trivalent lanthanoids actually decrease with increasing atomic number due to the lanthanoid contraction and poor shielding effect, which leads to a higher effective nuclear charge.

**Hint:** Recall that lanthanoid contraction affects ionic radii as atomic number increases.

### Step 4: Evaluate the Third Statement
**Statement 3:** "All lanthanoids are highly dense metals."
This statement is true. Lanthanoids have high atomic numbers and atomic masses, contributing to their high density. Lutetium, being the last member of the lanthanoid series, is the densest.

**Hint:** Think about the relationship between atomic mass and density in metals.

### Step 5: Evaluate the Fourth Statement
**Statement 4:** "Mostly typical oxidation state of lanthanoids is +3."
This statement is true. The most common oxidation state of lanthanoids is +3, which is achieved by removing two electrons from the outermost s orbital and one from the f orbital.

**Hint:** Consider the stability of the +3 oxidation state in terms of electron removal.

### Conclusion
After evaluating all statements, we find that the second statement is false. Therefore, the answer to the question is:

**Answer:** The false statement about lanthanoids is: "The ionic radii of trivalent lanthanoids steadily increases with the increase in atomic number."