Some elements have variable valancis. why​

Two friends at different locations want to communicate with each other by sending low energy signals. which of the following methods can they use to communicate? a) produce x-rays using colliding electrons and send them to radios, which capture sound b) send messages using infrared radiation, which travel in the form of waves c) send radio waves through intervening media like radio and television d) produce sound waves using microwaves from heated objects

How heavy is thanos? a) 3000 lbs b) all of it c) the price of tea in china d) heavy enough

How are isotopes of the same chemical element alike? how are they different?