Question: how many valence electrons does boron (b atomic no. = 5) have?
Answer: Boron has 5 electrons --- 2 in the first shell, and 3 in the second shell (so three valence electrons). Carbon has 6 electrons --- 2 in the first shell, and 4 in the second shell (so four valence electrons). Nitrogen has 7 electrons --- 2 in the first shell, and 5 in the second shell (so five valence electrons).