Q$1.$ Define followings

$($a$)$ isocratic elution.

$($b$)$ gradient elution.

$($c$)$ Eluent

$($d$)$ Eluate

Q$2.$ Explain the difference between gel filtration and gel permeation

Q$3.$ What types of species can be separated by HPLC but not by GC$?$

Q$4.$ Compare the advantages of HPLC and GC instruments.