The masses of the nucleus and the electron cloud of an atom is balanced if false. Do you have any answer options??
<span>The light spectrum that results from the light produced by an excited electron moving from a higher energy level back down to a lower energy level is an emission spectrum. The emission spectrum is formed by the electromagnetic radiation released by the transition in energy state.</span>
A!
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Answer : The value of rate constant is, 
Explanation :
First we have to calculate the rate constant, we use the formula :
Expression for rate law for first order kinetics is given by:

where,
k = rate constant = ?
t = time passed by the sample = 20 min
a = let initial amount of the reactant = 100 g
a - x = amount left after decay process = 100 - 85 = 15 g
Now put all the given values in above equation, we get


Therefore, the value of rate constant is, 
The boiling point depends on the strength of the intermolecular forces holding the molecules together. Greater the force, higher is the boiling point.
The intermolecular force increases in the order shown below:
ion-ion > H-bonding > dipole-dipole > London dispersion
CH3CN is a polar molecule with strong dipole-dipole forces
CH3CH2CH3 is non-polar held by london dispersion
Ar exist as a gas. It will have a lowest boiling point
Thus the order of decreasing b.pt is:
CH3CN > CH3CH2CH3 > Ar