Answer:
It is true that earth was once covered with oceans and little dry land.
Explanation:
Over the course of around four billion years, the Earth's oceans have lost about a quarter of their original mass. Today the atmosphere is rich in oxygen, which reacts with both hydrogen and deuterium to recreate water, which falls back to the Earth's surface. So the vast bulk of the water on Earth is held in a closed system that prevents the planet from gradually drying out. According to the researchers, the continents emerged relatively suddenly from an ocean that covered 95 percent of the Earth's surface. The appearance of large masses of dry land would have caused more extreme weather, changes in ocean currents and the emergence of proper seasons. In turn, these environmental changes may have led to rise in atmospheric oxygen that enabled the explosion of new life forms around 500 million years ago.
Answer: Option (a) is the correct answer.
Explanation:
A decomposition reaction is defined as a reaction where a compound dissociates into two or more atoms.
For example, 
Whereas a chemical reaction in which two reactants combine together to result in the formation of a compound is known as a synthesis reaction.
For example, 
is a synthesis reaction.
Thus, we can conclude that the statement chemical reaction A, because the reactant is a compound identifies the decomposition reaction and describes a substance is involved.
1s2 2s2 2p6 3s2 3p6 4s1
s orbital can hold 2 electron
p orbitals can hold 6 electron
The reaction is an exothermic one because heat is released to the surroundings. An exothermic reaction is a chemical reaction where energy is being released as the reaction by light or heat. On the other hand, endothermic reaction needs energy input for the reaction to proceed.
