An element can have atoms with different mass numbers but same chemical properties and some are also used in the field of medicine in the treatment of diseases.
-what are such element known as?
-define such elements and also write one example?
-give their one point of difference from isobars?

What are the major types of a chemical compound

Before it was launched, a helium-filled balloon had a pressure of 201 kpa at a temperature of 27°c. at an altitude of 15,000 m, the pressure had decreased to 2.5 kpa and the temperature had dropped to -14 °c. the volume of the balloon increased to 59.3 m3. what is the original volume of the balloon? 13 m3 0.85 m3 0.077 m3 1.17 m3

Areaction is first order. if the initial reactant concentration is 0.0200 m, and 25.0 days later the concentration is 6.25 x 10-4 m, then its half-life is: