How many methylene groups are present in 2,4-dimethylhexane?

Zero methylene groups

Explanation:

Hi, on one side you have the 2.4-dimethylhexane molecule as shown in the figure.

On the other side, you have the methylene group with the following structure:

=CH2

As can be seen there isn't any methylene group in the  2.4-dimethylhexane

Important: don't confuse the methylene group with the methyl group. Methyl group is -CH3 and there are two of them in this molecule.

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant.