The element which never acts as reducing agent in a chemical reaction is
A. $O$
B. $Li$
C. $F$
D. $C$

Hint: A compound or element which can donate its electron is called a reducing agent. A strong oxidising agent means it helps to oxidise other substances and itself get reduced. The element which has strongly bound electrons never acts as a reducing agent.

Complete Step by Step Answer:
The electronic configuration of $F$$is-$$1s^22s^22p^5$.
$F$ has $5$ electrons in a 2p shell. So, to get stability it needs one more electron and accepts one electron. Thus it acts as an oxidising agent not as a reducing agent.
The electronic configuration of $O$$is-$$1s^22s^22p^4$.
$O$ has $4$ electron in 2p shell. So, to get stability it releases one electron and acts as a reducing agent.
The electronic configuration of Li$is-$$1s^22s^1$.
Li has $1$ electrons in 2s shell. So, to get stability it needs one more electron and accepts one electron. Thus it acts as an oxidising agent.
The electronic configuration of $C$$is-$$1s^22s^22p^2$.
$C$ has $2$ electrons in a 2p shell. So, to get stability it needs one more electron and accepts one electron. Thus it acts as an oxidising agent.
The element which never acts as a reducing agent in a chemical reaction is$F$.
 Thus the correct option is C.

Note: Fluorine is the most reactive among the halogens due to strong electronegativity. Lithium is the most electropositive and highly reactive element due to presence of one electron in valence shell.