Identify the incorrect statement among the following

Options

A. There is decrease in the radii of atoms or ion as one proceeds from La to Lu
B. Lanthanoid contraction is the accumulation of successive shrinkages
C. As a result of lanthanide contraction, the properties of the 4th series of the contraction element have no similarities with the 5d series of elements
D. Shielding power of 4f element of electron is quite weak

Explanation

To solve the question of identifying the incorrect statement among the given options, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement:** "There is a decrease in the radius of atoms or ions as one proceeds from lanthanum to lutetium."

- **Explanation:** As we move from lanthanum (La) to lutetium (Lu) in the periodic table, we observe a decrease in atomic radius. This phenomenon occurs due to the increasing nuclear charge without a significant increase in shielding effect, leading to a stronger attraction between the nucleus and the electrons. Therefore, this statement is **correct**.

### Step 2: Analyze the second statement
**Statement:** "Lanthanide contraction accumulates successive shrinkage."

- **Explanation:** The term "lanthanide contraction" refers to the progressive decrease in the size of the lanthanide ions as we move from lanthanum to lutetium. This contraction is due to the poor shielding effect of the 4f electrons. Thus, this statement is also **correct**.

### Step 3: Analyze the third statement
**Statement:** "As a result of lanthanide contraction, the properties of the 4f series of elements have no similarity with the 5d series."

- **Explanation:** This statement is incorrect. Despite the lanthanide contraction, the properties of the 4f series (lanthanides) show similarities with the 5d series (transition metals), particularly in terms of ionic radii and some chemical properties. Therefore, this statement is **incorrect**.

### Step 4: Analyze the fourth statement
**Statement:** "The shielding power of 4f elements is weak."

- **Explanation:** The 4f electrons have a relatively poor shielding effect compared to other orbitals, which is true. However, this statement is somewhat misleading as it does not directly relate to the incorrectness of the other statements. Nonetheless, it is generally accepted that the shielding effect of 4f electrons is weak. Thus, this statement is **correct**.

### Conclusion
Based on the analysis, the incorrect statement is the third one: "As a result of lanthanide contraction, the properties of the 4f series of elements have no similarity with the 5d series."

### Final Answer
The incorrect statement is **option 3**.

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