is 3 ethyl 2 pentene a cis/trans isomerism?

Answer 1

No. 3-ethyl-2-pentene doesn't have cis-trans isomers because one of the carbon atoms of the double bond (C3) has two identical substituents (ethyl groups). Just look at the structure

CH3CH2.. .. ..CH3
.. .. .. .. ..\ .. ../
.. .. .. .. ..C=C
.. .. .. .. ../.. .. \
CH3CH2 ... .. H

So no matter where the -CH3 is (up or below the line of the double bond) there is no difference.