Answer:- B:
is the right answer.
Solution:- The balanced equation is:

We have been given with 8.75 grams of oxygen and asked to calculate the grams of hydrogen needed to react with given grams of oxygen according to the balanced equation.
From balanced equation, 1 mole of oxygen reacts with 2 moles of hydrogen.
So, let's convert grams of oxygen to moles and multiply it by the mole ratio to calculate the moles of hydrogen that are easily converted to grams on multiplying by it's molar mass.
The complete set up looks as:

= 
Hence, the right option is B:
.
When formaldehyde and acetone then react with each other( aldol condensation) then it will be formed <u> methyl vinyl ketone.</u>
<u />
In organic chemistry, an aldol condensation would be a condensation reaction in which an enol and enolate ion combines with a carbonyl chemical to produce a -hydroxy aldehyde or -hydroxy ketone, that is then dehydrated to produce a conjugated enone.
In aldol condensation, when formaldehyde and acetone then react with each other then it will be formed <u> </u><u>methyl vinyl ketone.</u>
It can be written as
→ 
When it will be heated then it gives methyl vinyl ketones.
→ 
So, the pair of reactants will be formaldehyde and acetone
To know more about aldol condensation
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Veces is Spanish word for times.Hope I helped.