The stability of alkenes is directly proportional to the number of α-hydrogen atoms due to hyperconjugation.
Let us count the number of α-hydrogen atoms in each given alkene:
A. 2-Methylbut-2-ene: (CH3)2C=CHCH3
Number of α-hydrogen atoms = 3+3+3=9
B. cis-But-2-ene: CH3CH=CHCH3
Number of α-hydrogen atoms = 3+3=6
C. 2,3-Dimethylbut-2-ene: (CH3)2C=C(CH3)2
Number of α-hydrogen atoms = 3+3+3+3=12
D. Prop-1-ene: CH3CH=CH2
Number of α-hydrogen atoms = 3
Since the stability of an alkene increases with the number of α-hydrogen atoms, the correct stability order is C > A > B > D.
Answer: C > A > B > D