The correct option is B III,IV,II,I
I has an sp2 hybridized carbocation which is highly unstable. Hence, I will be the least stable of all. III will be the most stable as it is tertiary carbocation.
Among II and IV, IV has 4 alpha− hydrogens whereas II has only, α− hydrogens. Also IV is a secondary carbocation while II is a primary one. Hence IV will be more stable than II.
Hence, the decreasing order of stability or stabilization energy is III>IV>II>I