B . microscope
this is the answer .
Answer: enthalpy of reaction.
Explanation:
Temperature of the gas is defined as the degree of hotness or coldness of a body. It is expressed in units like
and
Entropy is the measure of randomness or disorder of a system. If a system moves from an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.
Free energy is the amount of energy that can be converted into useful work.
Enthalpy of the reaction is the difference between the energy of products and the energy of reactants. it is either the heat released or absorbed during the reaction. It is either positive or negative.
These atoms and other atoms in group 8A have constant valence shell.it means that all of them have 8 electrons in their valence shell (except helium that has only 2 electrons )and they don't want to attract electrons.
that s why they don't have electronegativity.
hope this helps