<span>In the Bohr model electrons in atoms can occupy allowed orbits where they do not emit energy. Exchange of energy with the surrounding environment occurs only when an electron "jumps" from an orbit to another. Hope this answers the question. Have a nice day.</span>
Explanation:
21. The given molecule for cracking is tetradecane.
On cracking it forms one mole of decane (C10H22) and two moles of ethene gas.
The chemical equation is shown below:

22. The essential condition for the formation of an ester is the reaction of alcohol and acid in presence of concentrated sulfuric acid.
Thus among the given options, the first option is the correct one.
23. Isomers of butanol are shown below:
It is 2-butanol.
The position of -OH group changes to the second carbon.
Gay-Lussac's law gives the relationship between pressure and temperature of gas. For a fixed amount of gas, pressure is directly proportional to temperature at constant volume.
P/T = k
where P - pressure , T - temperature and k - constant

parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation
substituting the values in the equation

T = 4342 K
initial temperature was 4342 K
C. Magma from venus mantle erupted as lava.
Explanation:
A volcano is a land form which results from the eruption of molten rocks (lava) on the surface. Volcanic rocks are a special type of igneous rock that forms when molten rock cools and solidifies on the surface.
For a planet like Venus which is presently not active and little to no movement occurs within the plates, the volcanisim must have occurred when the planet was relatively young and it must have been millions of years ago.
It is widely believed that Venus was geologically active in times past. Mantle generated lava must have solidified on the surface in times past to have formed the volcano.
Evaluating other options:
Impact of space objects on Venus would lead to the formation of a crater which is a depression on the surface. The rock would be mostly metamorphic.
If water was ever present in Venus, they would have produced sedimentary rocks instead. The erosive power of water is not high enough to cut through the crust. Also, water would not aid the formation of volcanoes.
Heat is not enough to from volcanoes. Other factors are also in play.