An isotope of cesium (cesium-137) has a half-life of 30 years if 1.0g of cesium-137 disintegrates over a period of 90 years how many g of celsium-137 would remain

Asingle atom of an element has 21 neutrons, 20 electrons, and 20 protons. which element is it? ok o z

How do you convert 4 mmol of bromobenzene to ml?

Oil rich countries in the middle east cover about 4% of earths total land area but prossess about 48% of the worlds known oil reserves what is the main reason for high concentration of reserves in this part of the world