Isotopes of an element all have the same number of ___, and different number of ___.

List four observations that indicate that a chemical reaction may be taking place

Ascientist measures the speed of sound in a monatomic gas to be 449 m/s at 20∘c. what is the molar mass of this gas?

Answer asap : ( a. how does mucus prevent the entry of pathogens? b. describe two ways white blood cells protect us from pathogens.