Element X has 3 naturally occurring isotopes with the following masses and percent abundances: X-131 131.0012 19.2% X-134 134.0011 40.80% X-134 134.0009 40.00% What is the average atomic mass of element X?

A sample contains 4.761 moles of copper how many atoms of copper does the sample contain? 

A researcher has a sample of 0.0223 kg of substance how many micrograms (

Name the following compounds:  B2S4 [1] C3H8 [2] PSe2 [3]

An imaginary element sweetmonium (Sw) has an atomic mass of 61.22 g/mol. If you have 172.9 g of Sw how many moles would you have? 

A sample contains 3.857 moles of nickel how many atoms of nickel does the sample contain? 

Dark-line (absorption) spectra can be used to identify the ________ present in stars.

A comet is visible because ________.

The asthenosphere is the second layer of Earth characterized by ________.

Why did Galileo’s observation that Venus showed phases like the Moon indicate that the geocentric theory of the solar system was not possible?