In the periodic table all elements within the same group have the same

Step 1: Analyze the question The question asks what property is shared by all elements in the same vertical column (group) of the periodic table.

Step 2: The concept Elements in the same group have the same number of electrons in their outermost shell (valence electrons). This is why they react in similar ways and show similar chemical properties. For example:

• Group 1 (Li, Na, K): each has 1 valence electron
• Group 17 (F, Cl, Br): each has 7 valence electrons

Step 3: Check each option

• A. Number of neutrons: Wrong. Neutron numbers vary from element to element (Na has 12, K has 20).
• B. Number of valence electrons: Correct. Na (2,8,1) and K (2,8,8,1) both have 1 outer electron.
• C. Number of isotopes: Wrong. Different elements have different numbers of isotopes, and this has no link to group.
• D. Atomic number: Wrong. Atomic number is unique to each element, and it increases as you move down a group (Li = 3, Na = 11, K = 19).

Step 4: Answer The correct option is B. number of valence electrons.

Exam tip: Remember "Group = Valence electrons, Period = Number of shells." Elements in the same group share valence electrons, while elements in the same period share the same number of electron shells.