Question

Consider the following statements f-block elements.

(A) Uranium is the heaviest naturally occurring element (B) All actinoids are radioactive (C) Due to high radioactivity of actinoids, studies of their properties become difficult (D) All lanthanides are radioactive (E) From left to right in Lanthanide Series, ionic size (+3) decreases regularly

How many of the above statements is/are correct?

Answer 1

3

Answer 2

Let's analyze each statement:

• Statement (A): Uranium is the heaviest naturally occurring element.
  This is incorrect. While Uranium (Z=92) is the heaviest element found naturally in significant quantities, trace amounts of Neptunium (Z=93) and Plutonium (Z=94) are also naturally occurring. Plutonium-244 is heavier than Uranium-238.

• Statement (B): All actinoids are radioactive.
  This is correct. All isotopes of all actinoid elements are unstable and undergo radioactive decay.

• Statement (C): Due to high radioactivity of actinoids, studies of their properties become difficult.
  This is correct. The high radioactivity necessitates specialized equipment and stringent safety protocols.

• Statement (D): All lanthanides are radioactive.
  This is incorrect. Most lanthanides have stable isotopes. Only Promethium (Pm, Z=61) is entirely radioactive.

• Statement (E): From left to right in Lanthanide Series, ionic size (+3) decreases regularly.
  This is correct. This phenomenon is known as lanthanide contraction.

Therefore, statements B, C, and E are correct, making a total of 3 correct statements.