Question
An element is in group 4 and period 3 of the periodic table. How many electrons are in the highest occupied energy level of an atom of this element?
A. 3
B. 4
C. 12
D. 14
▶️Answer/Explanation
B
The element is Hf : [Xe] 4f14 5d2 6s2
Group 4 elements are transition elements. In this case, we need to consider the electrons in the highest occupied energy level (n) plus the electrons in the (n-1) d orbital.
Electrons in highest occupied energy level or valence electrons = 2+2 =4.
Question
Which statements about atomic structure and the periodic table are correct?
I. An element in group 2 has 2 electrons in its valence (outer) energy level.
II. An element in period 3 has electrons in 3 energy levels.
III. The element in group 2 and period 3 has an atomic number of 12.
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
▶️Answer/Explanation
D
Group 2 elements have ns2 electronic configuration of outer shell, where n is the period number. Hence, they have 2 electrons in its valence (outer) energy level.
Elements in period 3 go up to n=3. Hence, they have 3 energy levels.
The element in group 2 and period 3 have electronic configuration of outer shell as 3s2 .Which means it has electronic configuration of 1s22s22p63s2 . Its atomic number is 12. It is Mg.
Question
Element X is in group 5 and period 4 of the periodic table. Which statement is correct?
A. X has 5 occupied energy levels.
B. X can form ions with 3+ charge.
C. X is not a transition element.
D. X has 4 valence electrons.
▶️Answer/Explanation
B
Element is in period 4, it will have n=1 up to n=4. X occupies 4 energy levels.
Since it is in period 4, group 5, it is a transition element and it has electronic configuration of 1s2 2s2 2p6 3s2 3p6 3d3 4s2 and it has 3+2 = 5 valence electrons.
It can form ions up to 5+ charge.
Question
Which property increases down Group 1, the alkali metals?
A. Atomic radius
B. Electronegativity
C. First ionization energy
D. Melting point
▶️Answer/Explanation
A
Atomic radius increases down the group as n increases from top to bottom.
Question
Which element is a lanthanide?
A. Hf
B. Tb
C. U
D. Y
▶️Answer/Explanation
B
The lanthanide or lanthanoid series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium.
Tb Terbium with atomic number 65 is a lanthanide.
Question
Which element is in the p-block?
A. Pb
B. Pm
C. Pt
D. Pu
▶️Answer/Explanation
A
Out of these, Pb is in the p-block.