The strongest base is

Options

A. `Ce(OH)_(3)`
B. `Lu(OH)_(3)`
C. `Yb(OH)_(3)`
D. `Pm(OH)_(3)`

Answer

To determine the strongest base among the lanthanide series, we need to analyze the basic strength of their hydroxides. Here’s a step-by-step solution:

### Step 1: Identify the Elements
The question refers to elements in the lanthanide series. The lanthanides include elements from Lanthanum (La) to Lutetium (Lu).

### Step 2: Understand Oxidation States
In this case, we are considering the trivalent ions (M^3+) of these elements, which means we will be looking at La^3+, Ce^3+, Yb^3+, Pm^3+, and Lu^3+.

### Step 3: Analyze Basic Strength of Hydroxides
The basic strength of hydroxides of lanthanides decreases as we move from La to Lu. This is due to the following reasons:
- As we move from La to Lu, the atomic number increases.
- With an increase in atomic number, the size of the ions decreases.
- The decrease in size is due to an increase in nuclear charge, which pulls the electrons closer to the nucleus.

### Step 4: Relate Size to Basicity
The basicity of hydroxides is inversely related to the covalent character of the hydroxides. As the size of the ion decreases, the covalent character increases, leading to a decrease in basic strength.

### Step 5: Conclusion
Thus, La(OH)3 is the most basic hydroxide among the lanthanides, while Lu(OH)3 is the least basic. Therefore, the strongest base among the given options is La(OH)3.

### Final Answer
The strongest base is **La(OH)3**.

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