Answer: M-18
Explanation:
The mass spectra of alcohols often fail to exhibit detectable M peaks but instead show relatively large __M-18___ peaks.
Mass spectroscopy is used to determine the molecular mass and molecular formula of a sample.
When the mass spectra of alcohols do not show detectable M peaks, they show relatively large M-18 peaks.
One mole of methane has a mass of 16 g
Answer : The correct option is, (B) 
Solution :
According to the Graham's law, the rate of effusion of gas is inversely proportional to the square root of the molar mass of gas.
or,
..........(1)
where,
= rate of effusion of unknown gas = 
= rate of effusion of oxygen gas = 
= molar mass of unknown gas = ?
= molar mass of oxygen gas = 32 g/mole
Now put all the given values in the above formula 1, we get:
The unknown gas could be carbon dioxide 
that has approximately 44 g/mole of molar mass.
Thus, the unknown gas could be carbon dioxide
