boron has two naturally occurring isotopes .there are 10 b(20%)and 11b(80%).what is the average atomic mass of boron

Explanation:

Average Atomic mass of any element =[ ∑ Abundance* mass of element] /100

                                                                = 10*20 +11*80 /100

                                                                =

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a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.