The elements with atomic numbers 101 and 104 belong to, respectively :

Solution

Chemistry ma’am · 4 steps

Mark the actinoid span 90 to 103, then count the 6d metals onward from group 4 after it.

1. Actinoid range. The actinoids follow actinium (89) and run from thorium (90) to lawrencium (103). In these elements the 5f orbitals are being filled.
2. Element 101. Mendelevium (Md, 101) lies between 90 and 103, so it is an actinoid.
3. Element 104. After lawrencium, the 6d series begins in group 4, and each next element moves one group to the right. Rutherfordium (Rf, 104) is the first of these, so it sits in group 4, below Ti, Zr and Hf.

   Atomic number	Element	Position
   101	Mendelevium (Md)	Actinoid
   104	Rutherfordium (Rf)	Group 4
   106	Seaborgium (Sg)	Group 6
   111	Roentgenium (Rg)	Group 11

4. So. Element 101 is an actinoid and element 104 is in group 4. That matches option (b).

The idea to keep. Actinoids are 90 to 103. After them, the 6d series starts in group 4, so for elements from 104 onward, the group number is the atomic number minus 100.

Answer from the NTA final answer key. Solution by PrepWiser.