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Current Question (ID: 18888)

Question:

$\text{The consequence(s) of lanthanoid contraction is/are:}$

Options:

1. $\text{Similarity in the properties of second and third transition series.}$
2. $\text{Separation of lanthanoids is difficult.}$
3. $\text{Variation in the basic strength of lanthanide hydroxides.}$
4. $\text{All of the above.}$

Solution:

$\text{Hint: f-orbital electrons have a poor shielding effect.}$ $\text{Explanation:}$ $\text{Step 1: What is Lanthanoid contraction?}$ $\text{As we move along the lanthanoid series, the atomic number increases gradually by one. This means that the number of electrons and protons present in an atom also increases by one.}$ $\text{As electrons are being added to the same shell, the effective nuclear charge increases. This happens because the increase in nuclear attraction due to the addition of proton is more pronounced than the increase in the interelectronic repulsions due to the addition of electrons.}$ $\text{Also, with the increase in atomic number, the number of electrons in the 4f orbital also increases.}$ $\text{The 4f electrons have a poor shielding effect. Therefore, the effective nuclear charge experienced by the outer electrons increases. Consequently, the attraction of the nucleus for the outermost electrons increases.}$ $\text{This results in a steady decrease in the size of lanthanoids with an increase in the atomic number. This is termed lanthanoid contraction.}$ $\text{Step 2: Consequences of lanthanoid contraction}$ $\text{(i) Due to lanthanoid contraction, the change in the atomic or ionic radii of these elements is very small. Hence, their chemical properties are similar. This makes their separation difficult.}$ $\text{(ii) It is due to lanthanoid contraction that there is variation in the basic strength of lanthanide hydroxides. (Basic strength decreases from La(OH)}_3 \text{ to Lu(OH)}_3\text{).}$

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Expected JSON Format:

{
  "question": "The mass of carbon present in 0.5 mole of $\\mathrm{K}_4[\\mathrm{Fe(CN)}_6]$ is:",
  "options": [
    {
      "id": 1,
      "text": "1.8 g"
    },
    {
      "id": 2,
      "text": "18 g"
    },
    {
      "id": 3,
      "text": "3.6 g"
    },
    {
      "id": 4,
      "text": "36 g"
    }
  ],
  "solution": "\\begin{align}\n&\\text{Hint: Mole concept}\\\\\n&1 \\text{ mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6] = 6 \\text{ moles of carbon atom}\\\\\n&0.5 \\text{ mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6] = 6 \\times 0.5 \\text{ mol} = 3 \\text{ mol}\\\\\n&1 \\text{ mol of carbon} = 12 \\text{ g}\\\\\n&3 \\text{ mol carbon} = 12 \\times 3 = 36 \\text{ g}\\\\\n&\\text{Hence, 36 g mass of carbon present in 0.5 mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6].\n\\end{align}",
  "correct_answer": 4
}