What percentage do the elements hydrogen and helium account for in the universe? A. 100% B. 99.9% C. 98% D. 99.8%

Which of the following would most likely result in an increase in reaction rate? placing the reactants on a hotplate placing the reactants in an ice bath placing the products in an ice bath

What two properties of an electron did robert millikan determine?

What is a good definition for "reactivity with vinegar"?

Emily spills concentrated sodium hydroxide solution on her lab bench. what she should do first

List two observations that could be evidence of a chemical reaction.

Why does the effective nuclear charge increase across a row of the periodic table?

Iodine-131 decays to form xenon-131. the half-life of this reaction is 8.07 days. from a 200-g sample of iodine-131, how much of the sample is xenon-131 after 16.14 days?

Complete the following statement by checking all that apply Creativity allows scientists to develop multiple approaches to solving problems. adapt to changes in scientific knowledge. look at old problems in new ways.

The atomic weight of hydrogen is 1.00794. a. True b. False

Describe What kind of ions do metals form? What kind of ions do nonmetals form?