First small- $(1+000000000*2^{-9})*2^{0-31}= 1*2^{-31}= 2^{-31}$
Second small- $(1+000000001*2^{-9})*2^{0-31}= 1*2^{-31}+ 1*2^{-9}*2^{-31}= 2^{-31}+2^{-40}$
Difference - $2^{-40}$
If IEEE 754 is mentioned then for minimum we can't take E = 000..0 as E = 0 is reserved for special number.