Final answer:
The pair of elements with the same number of valence electrons is a) Be and Mg, as they are both alkaline earth metals belonging to Group 2 of the periodic table and have two valence electrons.
Step-by-step explanation:
The question asks which pair of elements would have the same number of valence electrons. Elements in any one group (or column) of the periodic table have the same number of valence electrons due to their similar outer electron configurations, which leads to similar chemical properties. For the options provided:
- a) Be and Mg - Both Beryllium (Be) and Magnesium (Mg) are members of the alkaline earth metals and are in Group 2 of the periodic table. Therefore, they each have two valence electrons.
- b) Li and Na - These are alkali metals and are in Group 1, so they have one valence electron.
- c) Na and Mg - Sodium (Na) is an alkali metal (Group 1) with one valence electron while Magnesium (Mg) is an alkaline earth metal (Group 2) with two valence electrons, hence they do not have the same number.
- d) Li and B - Lithium (Li) is an alkali metal with one valence electron, and Boron (B) is in Group 13, so it has three valence electrons.
Based on this information, the correct answer is a) Be and Mg, as these elements have the same number of valence electrons.