If an atom has 34 protons and 40 neutrons, what is its mass number? 40 6 74 34

I'm learning about the periodic tables and what each subject's configuration is. for example, hydrogen is 1s^1, but i don't understand how you get that. can someone me understand how to figure out how to figure this out? sorry if the question makes no sense, but it would really a lot if you could me understand! you so much if you can!

How many moles of oxygen gas are produced from the decomposition of six moles of potassium chlorate

How many joules of heat are required to raise thetemperature of 750 g of water from 11.0 °c to 19.0 °c?