Làm sao để tính số e trong nguyên tử và số e ở lớp ngoài cùng ạ

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

Which formula can be used to calculate the molar mass of ammonia (nh3)? molar mass of n + molar mass of h 3 × molar mass of n + molar mass of h molar mass of n + 3 × molar mass of h 3 × molar mass of n + 3 × molar mass of h

Calculate - analysis of compound composed of iron and oxygen yields 174.86 of fe and 75.14g of o. what is the empirical formula for this compound?