In a sample of 1000 atoms of an unknown element, it is found that 14 are isotopes of mass 203.973 amu, 241 are isotopes of mass 205.9745, 221
are isotopes of mass 206.9759, and the remaining 524 are isotopes of
mass 207.9766 amu.
1. Calculate the average atomic mass of the unknown substance. Answer
with four decimal places
1. Determine the identity of the unknown element.

How much heat is added if 0.814g of water increase in temperature by 0.351 degree c?

15. which of the following is not human-caused groundwater pollution? a. water in an aquifer dissolves elements such as arsenic and mercury from surrounding rock. b. water in an aquifer is contaminated by leachate that seeps into the ground from a landfill. c. water in an aquifer becomes polluted with chemicals used in hydraulic fracturing, or fracking. d. water in an aquifer absorbs harmful bacteria from the drainage field of a septic tank.

All chemicals, even safe chemicals, such as sodium chloride( table salt), are toxic if exposure is high enough. (true or false)