​Sheep RBCs (SRBCs) were added in wells 1-10 of a micro-titre plate as shown in the figure below. Next, serum from a mouse that had been immunized with SRBCs was diluted 1/50 in a tube and then added in serial two-fold dilutions from wells 1-9.​

​Which of the following statements is correct about titre of anti-SRBC antibodies in the serum sample?​

Correct option is A

The correct answer is (a).
The titre corresponds to the highest dilution at which agglutination is still visible. Based on the serial two-fold dilution and agglutination pattern, if agglutination is seen in well 4 (1/400 dilution) and not in well 5 (1/800 dilution), the titre of the antibodies is 1/400.
Incorrect options-
Option (b) 1/6 is incorrect because no such dilution series was made, and 1/6 does not fit the dilution pattern.
Option (c) 1/800 is incorrect since there is no visible agglutination in well 9, which corresponds to this dilution.
Option (d) 1/8 is incorrect as it is not consistent with the initial serum dilution or the serial two-fold dilution steps.