Classify the following species as electrophile or nucleophle and explain your choice:
(i) `CH_(3)overset(* *)underset(* *)(O):^(Theta)`
(ii) `CH_(3)COoverset(* *)underset(* *)(O):^(Theta)`
(iii) `:overset(* *)underset(* *)(Cl^(oplus)`
(iv) `BF_(3)`
(v) `(CH_(3))_(3)overset(oplus)(C)`
(vi) `CH_(2) = CH_(2)`
(vii) R - X

Explanation

Nucleophile : `CH_(3)O^(-) , CH_(3)COO^(-),CH_(2)=CH_(2)` Electropile : `CI^(+),BF_(3),(CH_(3))_(3)C^(+),R-XCH_(3)O^(-)andCH_(3)COO^(-)` are negatively charged species having available unshared electron pair O - atom. So these are nucleophiles. `CH_(2) = CH_(2)` can also act as a nucleophile as it contains loosely bounded `pi` - electrons.
In the species `CI^(+), BF_(3) and Me_(3)C^(+)`, there are electron deficiency (having sextet of electron) on the valence - shells of CI, B and C - atom respectively. So these are electrophiles. In the alkyl halides `(overset(delta+)(R)-overset(delta+)(X))` there is electron deficiency on the `alpha` - carbon due to strong -I effect of halogen atom. So RX can act as electrophile.