The clinical test that is used for diagnosis of typhoid is:

The correct option is B Widal

$ELISA$

Enzyme linked immunosorbent assay ($ELISA$) is a technique based on the principle of antigen-antibody interaction. It is used to measure the amount of proteins or detect antibodies in samples.

$ESR$

Erythrocyte sedimentation rate ($ESR$) is a technique to find the sedimentation rate of $RBCs$. It is used to detect inflammation due to diseases like infections, cancer etc.

$PCR$

Polymerase chain reaction ($PCR$) is a technique involving amplification of a segment of $DNA$. It can be used to detect a virus in a sample.

Widal test

The Widal test detects the $O$ and $H$ antibodies of $S$. typhi. A patient suffering from typhoid produces antibodies against the $O$ and $H$ antigens. When their sera is taken for testing, the antibodies present in it get clumped with the antigens present in the Widal kit. This forms prominent observable complexes.

Final answer

d. Widal test