Which of the following statements does not accurately describe precambrian earth? a. the atmosphere was similar to that of early mars and venus. b. the oceans were chemically different from modern oceans. c. the ocean water was salty and rich in dissolved oxygen. d. there were large amounts of water in earth’s mantle.

C. The ocean water was salty and rich in dissolved oxygen.  

Explanation:

The oldest and longest of the Geological Ages, the Pre-Cambrian extends from the formation of the Earth, approximately 4.5 billion years ago, to 570 million years ago.

This period begins with the formation of the Earth about 4.5 billion years ago, where the Earth was an incandescent mass with rivers of dissolved rock, erupting volcanoes and large amount of sulfur. The atmosphere was initially similar to the atmosphere of Mars and Venus and was composed of nitrogen, ammonia, hydrogen, carbon monoxide, methane and water vapor, expelled by volcanoes, and no sign of oxygen.

After 700 million years, most of the rocks on the surface of the earth had already been cooled and a large amount of water had condensed into an ocean. Even so, the volcanic eruptions were still constant and were giving rise to several islands that were pushed toward each other by the movement of the mantle. In this period small unicellular beings in the ocean begin to appear, the primitive algae and bacteria that assimilate the carbon dioxide of the atmosphere transforming it into free oxygen, slowly changing the composition of the atmosphere that, in that period, was composed basically by nitrogen and steam of Water. They are of this period the oldest fossils of the earth.

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol