Identifying secondary alcohol yielding C5H10 alkene via dehydration

Steps:

• Dehydration removes H2O (MW 18) from alcohol, so target alkene M+ 70 implies alcohol MW 88 (C5H12O).
• Secondary alcohol has OH on carbon bonded to two other carbons.
• Confirm alkene formula: C5H10 (512 + 101 = 70) fits general alkene CnH2n.
• Match options to C5H12O secondary alcohols like pentan-2-ol or 3-methylbutan-2-ol.

Why B is correct:

• B is a C5H12O secondary alcohol (OH on secondary carbon), dehydrates to C5H10 (M+ 70) per Zaitsev's rule.

Why the others are wrong:

• A: Primary alcohol, not secondary.
• C: Tertiary alcohol, dehydrates but not secondary.
• D: Not C5H12O (wrong MW or structure).

Not enough information on exact structures for choices.

Final answer: B