Question

Given,14 elements after actinium are called
A.Lanthanides
B.Actinides
C.d-block elements
D.p-block elements

Answer 1

Each of the options given above has a unique set of elements in it, so identifying each of them will make it easier to get the answer for the question. Some series of elements are named after the first element it has, because the rest of the element in that series behaves similarly.

Complete answer:
The correct answer to this question is option B, the 14 elements after actinium are called Actinides. Let us see what each of the options stands for to understand the answer in a better way.
First, let us see the series of elements lanthanides includes. Lanthanides are those elements which are in between atomic number 57 and 71. All the elements between atomic number 57 and 71 come under lanthanide series.
The series of lanthanides starts from element lanthanum which has the atomic number 57 and ends at the element lutetium which has the atomic number 71.
Second, actinides are those elements which are in between 89 and 103, starting from the element actinide which has the atomic number 89 and ending with the element lawrencium which has the atomic number 103.
Groups that come under atomic number 3 to 12 of the periodic table are called d-block elements. They are called d-block elements because d subshells are filled in the elements that come under d-block.
Groups that come under atomic number 13 to 18 of the periodic table are called p-block elements. They are called p-block elements because p subshells are filled in the elements that come under p-block.
Thus, only one option satisfies our answer to the question, which is option B.

Note:
In lanthanides, 4f orbitals are filled and in actinium, 5f orbitals are filled. To get the answer to this question, the knowledge of the periodic table is necessary. Without knowing about lanthanides and actinides, the answer cannot be obtained. Although the lanthanide series starts from cerium to complete the 14 elements, and actinium series starts with thorium, lanthanum and actinium are included in the series despite lacking f orbitals.