1. What is the atomic mass of hydrogen if 99.985% is hydrogen-1 and 0.015% is hydrogen-2?

The atomic mass of Hydrogen : 1.02985

Isotopes are elements that have the same Atomic Number (Proton)  

Atomic mass is the average atomic mass of all its isotopes  

In determining the mass of an atom, as a standard is the mass of 1 carbon-12 atom whose mass is 12 amu  

An atomic mass unit = amu is a relative atomic mass of 1/12 the mass of an atom of carbon-12.  

Mass atom X = mass isotope 1 . % + mass isotope 2.% ..

99.985% is hydrogen-1 and 0.015% is hydrogen-2

The atomic mass of Hydrogen :

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

the answer is c i took the test