Which pair of atomic numbers represents elements in the same group?

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11, 19 Explanation: Elements in the same group share the same number of valence electrons and exhibit similar chemical properties. To find the group, we look at the electronic configuration: • Atomic number 11 (Sodium, Na): Configuration is 2, 8, 1. It has 1 valence electron (Group 1). • Atomic number 19 (Potassium, K): The configuration is 2, 8, 8, 1. It also has 1 valence electron (Group 1). Since both have 1 valence electron, they belong to the same group (Group 1, the Alkali Metals).

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