Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a suitable method. Give reason.

(N/A) The formation of ethers by acid-catalyzed dehydration of alcohols is a bimolecular nucleophilic substitution $(S_N2)$ reaction,which involves the attack of an alcohol molecule on a protonated alcohol molecule.
For this reaction to occur,the alkyl group of the alcohol must be unhindered to allow the nucleophilic attack.
In the case of secondary or tertiary alcohols,the alkyl group is sterically hindered.
Due to this steric hindrance,the elimination reaction (forming alkenes) becomes more favorable than the substitution reaction (forming ethers).
Therefore,acid dehydration of secondary or tertiary alcohols primarily yields alkenes instead of ethers.