If Y. M (Young Modulus) of a material is less, then the Stress' value of that material is going to be less too, right? Because Y.M= Stress/ Strain Y.M is directly proportional to Stress
(Just want to quickly make sure if that's really right)
No. (please note this answer too @ukii ) The Y.M of a material is defined as stress/strain - that much is true. You are looking at this from the wrong point of view. The amount of strain a material undergoes when you apply a stretching force is directly proportional the the stress stress = Y.M x strain (YM is the constant.) the amount of stress a material is under is directly proportional to the amount of strain it has experienced Strain = (1/YM) x Stress the constant is 1/YM
But YM = stress/strain - but stress and strain are related YM could only be directly proportional to stress if the strain remained constant - but it doesn't. When the apply stress you get strain. Strain is not constant under changing stress.
The Young Modulus is not really proportional to anything (at this level) it's a constant. It depends on both stress and strain. In terms of the reason why the YM value for a material is what it is, you have to look at the interatomic or intermolecular forces with it.