Answer:

Explanation:
Given that:
The Half-life of
=
is less than that of 
Although we are not given any value about the present weight of
.
So, consider the present weight in the percentage of
to be y%
Then, the time elapsed to get the present weight of
= 
Therefore;

here;
= Number of radioactive atoms relating to the weight of y of 
Thus:

--- (1)
However, Suppose the time elapsed from the initial stage to arrive at the weight of the percentage of
to be = 
Then:
---- (2)
here;
= Number of radioactive atoms of
relating to 3.0 a/o weight
Now, equating equation (1) and (2) together, we have:

replacing the half-life of
=
( since
)
∴

The time elapsed signifies how long the isotopic abundance of 235U equal to 3.0 a/o
Thus, The time elapsed is 
Answer : The mole fraction of NaCl in a mixture is, 0.360
Explanation : Given,
Moles of
= 7.21 mole
Moles of
= 9.37 mole
Moles of
= 3.42 mole
Now we have to calculate the mole fraction of
.

Now put all the given values in this formula, we get:

Therefore, the mole fraction of NaCl in a mixture is, 0.360
C3H8 + O2 --> CO2(g) + H2O(g) + energy(heat)
butane + oxygen --> carbon dioxide + water + heat
Propylethylene would be the answer
The answer is C. Nicotine is the substance found in tobacco smoke that stimulates the brain.