What is a covalent bond?​

Answer;

Banded iron formations

Before free oxygen gas became abundant in the oceans and atmosphere, it reacted with a metal and produced banded iron formations.

Explanation;

• Cyanobacteria are thought to have introduced oxygen into the early atmosphere. This was important because oxygen played a key role in the evolution of eukaryotic organisms creating an ozone layer to shield life from UV rays.
• Banded iron layers were formed in sea water as the result of oxygen released by the photosynthetic cyanobacteria.  As the photosynthetic organisms released oxygen, the available iron in the Earth's oceans precipitated out as iron oxides.

Answer:

no

Explanation:

it is not endothermic reaction

Answer:

The correct statement is option c, that is, particles discharged in the air by volcanoes fall to the ground and enrich the soil.  

Explanation:

The eruptions of volcanoes lead to the dispersion of ash over the broader regions surrounding the site of eruption. On the basis of the chemistry of the magma, the ash will be comprising different concentrations of soil nutrients. While the major elements found in the magma are oxygen and silica, the eruptions also lead to the discharging of carbon dioxide, water, hydrogen sulfide, sulfur dioxide, and hydrogen chloride.  

In supplementation, the eruptions also discharge bits of rocks like pyroxene, potolivine, amphibole, feldspar that are in turn enriched with magnesium, iron, and potassium. As an outcome, the areas which comprise huge deposits of the volcanic soil are quite fertile.  

Answer:

Option (C)

Explanation:

The volcanic eruptions are usually very destructive but it also has some advantages of which, one is that it makes the soil fertile in the nearby region.

During the time of the volcanic eruption, a large number of pyroclastic materials, blocks and ashes that are comprised of various gases are released, which eventually adds to the soil of the nearby areas. These materials ejected from the volcano are rich in various minerals such as oxygen, silicon, and some amount of CO₂, SO₂, and HCl which facilitates the growth of the soil and increases its productivity.

Thus, the soil around a volcanic region is much fertile.

Hence, the correct answer is option (C).