Arrange the following in decreasing order of basic strength 

(I) CH₃CHTMgBr                   (II) H-C$\equiv$CMgBr
(III) CH₃CH₂OMgBr            

The best way to compare their basic strength is to compare the acidic strength of their conjugate acid and then reverse the order
because there is inverse relation in the strength of conjugate pair. The order of acidic strength of conjugate acid is 

${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}<\mathrm{H}-\mathrm{C}\equiv \mathrm{C}-\mathrm{H}>{\mathrm{CH}}_3{\mathrm{CH}}_3$

$\therefore \mathrm{Decreasing} \mathrm{order} \mathrm{of} \mathrm{basic} \mathrm{strength} \mathrm{is}$

${\mathrm{CH}}_3{\mathrm{CH}}_2^{-}>\mathrm{H}-\mathrm{C}\equiv {\mathrm{C}}^{-}>{\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{O}}^{-}$