Multiple Choice
Which two elements were discovered by Pierre and Marie Curie?
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2. Atoms & Elements
Periodic Table: Representative Elements & Transition Metals
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How many elements are present in period 4 of the periodic table?
A
16
B
8
C
10
D
18
Verified step by step guidance1
Understand that a period in the periodic table corresponds to a horizontal row, where elements have the same principal energy level (n).
Recall that period 4 starts with potassium (K) and ends with krypton (Kr), covering elements with electrons filling the 4th energy level and the 3d subshell.
Count the elements in period 4 by including all s-block, d-block, and p-block elements in that row: 2 elements in the 4s subshell, 10 elements in the 3d subshell, and 6 elements in the 4p subshell.
Add these numbers together: 2 (4s) + 10 (3d) + 6 (4p) = 18 elements in total in period 4.
Confirm that the total number of elements in period 4 is 18, which matches the correct answer.
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