When do you use parentheses in writing a chemical formula?

Sex cells from female reproductive organ? 1) mitosis 2) fertilization 3) zygote 4) eggs 5) meiosis 6) sperm

Name the element in group 17, period 2. (periodic table)

Suppose you have designed a new thermometer called the x thermometer. on the x scale the boiling point of water is 129 ? x and the freezing point of water is 13 ? x. part a at what temperature are the readings on the fahrenheit and x thermometers the same?