Scientists have hypothesized that oxygen began to build up in the Earth's atmosphere after the development of living things with the ability to

a. breathe air.

b. form tissues.

c. photosynthesize.

d. reproduce sexually.

How many valence electrons do the inert gases have? a. 1 c. 5 b. 4 d. 8

Suppose the amount of a certain radioactive substance in a sample decays from to over a period of days. Calculate the half life of the substance. Round your answer to significant digit.

Element "yellowium" has three naturally occurring isotopes. Below are the masses and relative abundance of each isotope. Find the average atomic mass of yellowium. yellowium-15 15.012 amu 14.23% yellowium-17 16.988 amu 33.48% yellowium-19 19.

A student is given a mixture that he is told consists of two pure substances. the mixture is a clear liquid. the student is able to seperate the mixture only through distilation.

After 1911, most scientists accepted the theory that nucleus of an atom was very dense and very small and has a positive charge. What led scientists to accept this theory?

A nonvesicular rock is made entirely of green 2-millimeter-diameter crystals that have a hardness of 6.5 and show fracture, but not cleavage. The rock is most likely

What is the mass of 2.13 moles of lithium arsenate

What is the name fro H2O

A scientist has a tomato plant with red-skinned tomatoes. It has one allele for red skin (R) and one for yellow skin (r). Which describes the phenotype of the tomato plant?

Which of the following sentence best describes a buffer? A. Buffer is A substance that resists small change in the acidity of a solution when an acid or base is added to the solution. B.