1) The percentage of oxygen in dry air is A. 0.1
B. 1.0
C. 21
D. 79

2) The composition of the Earth’s earliest atmosphere was different to that of the present atmosphere. Which of these gases was present in large amounts in the Earth’s earliest atmosphere?

A. Oxygen
B. Carbon dioxide
C. Ammonia
D. Nitrogen

1) The percentage of oxygen in dry air is

C. 21

2) The composition of the Earth’s earliest atmosphere was different to that of the present atmosphere. Which of these gases was present in large amounts in the Earth’s earliest atmosphere?

B. CARBON DIOXIDE

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The percentage of oxygen in dry air is .  21

Explanation:  Ammonia gases was present in large amounts  in the easth7s earliest atmosphere

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answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.