Question

Element X, Y and Z have atomic number 19, 37 and 55 respectively. Which of the following statements is true about them

• A. Z would have the highest ionization potential
• B. Their ionization potential would increase with increasing atomic anumber
• C. Y would have the highest ionization potential
• D. Y would have an ionization potential between those of X and Z

Answer 1

The Correct Option is D

Correct Answer: Y would have an ionization potential between those of X and Z
 
Explanation:
• The elements X (Z = 19), Y (Z = 37), and Z (Z = 55) are all alkali metals: 
→ X = Potassium (K), Y = Rubidium (Rb), Z = Cesium (Cs)

• In a group, as atomic number increases (going down the group), the atomic size increases.
• As a result, the outermost electron is farther from the nucleus and is more easily removed.
• Therefore, ionization potential decreases down the group.

So the correct order is:
Ionization Potential: K (X) > Rb (Y) > Cs (Z)

Hence, Y (Rubidium) would have an ionization potential between those of X and Z.

Answer 2

The ionization potential refers to the energy required to remove an electron from an atom or ion. It generally increases across a period (from left to right) in the periodic table and decreases down a group (from top to bottom).
Given the atomic numbers of the elements:
X (atomic number 19) corresponds to potassium (K)
Y (atomic number 37) corresponds to rubidium (Rb)
Z (atomic number 55) corresponds to cesium (Cs)
Based on their positions in the periodic table, we can make the following observations:
(1) Z would have the highest ionization potential: This statement is incorrect. In general, ionization potential tends to decrease down a group in the periodic table. Since cesium (Z) is at the bottom of Group 1, it would have a lower ionization potential compared to potassium (X) and rubidium (Y).
(2) Their ionization potential would increase with increasing atomic number: This statement is incorrect. As mentioned earlier, ionization potential generally increases across a period from left to right, not with increasing atomic number.
(3) Y would have the highest ionization potential: This statement is incorrect. Following the trend mentioned above, rubidium (Y) would have a lower ionization potential compared to cesium (Z) and potassium (X).
(4) Y would have an ionization potential between those of X and Z: This statement is correct. Considering the trend of increasing ionization potential across a period, we can conclude that rubidium (Y) would have an ionization potential higher than potassium (X) but lower than cesium (Z).
Therefore, the correct statement is (4) Y would have an ionization potential between those of X and Z.