Explanation:
Grignard reagent is an organometallic compound, typically represented by the general formula RMgX, where R is an organic group and X is a halogen, usually chloride, bromide or iodide. The reactivity of Grignard reagents is due to the high polarity of the carbon-magnesium bond, which makes the carbon atom highly nucleophilic.

When Grignard reagents react with alcohols, they undergo a nucleophilic substitution reaction to form alkanes. The reaction mechanism involves the formation of an intermediate alkoxide species, which then undergoes a protonation step to produce the alkane.

Reaction:
The reaction between a Grignard reagent and an alcohol can be represented by the following general equation:
R-Mg-X + R'-OH → R-R' + MgX(OH)

Where R and R' can be any organic group.

Number of Grignard reagents:
In order to produce n-butane (CH3CH2CH2CH3), which is a four-carbon alkane, we need to use two Grignard reagents, each with two carbons. The two Grignard reagents react with two molecules of alcohol to form two different alkoxides, which then react with each other to produce n-butane.

This can be represented by the following equation:
2R-Mg-X + 2R'-OH → R-R' + R-R' + MgX(OH)2

Therefore, the answer is (2) 2 Grignard reagents are required to produce n-butane from alcohols.

2.. the possible Grignards are 

CH3CH2CH2CH2MgX 

CH3CH2CH2CH3 
.............| 
.............MgX