In a demonstration to find out the food sample being tested, 1cm3 of dilute sodium hydroxide solution was added to 3cm3 of test solution drop wise. The test tube was shaken thoroughly. A purple colour was observed at the end. Which food substance was being tested and what is the name of the test?

Both parents have blood group AB. Blood group AB is a result of codominance between the $I^A$ and $I^B$ alleles. Therefore, the genotype for blood group AB is $I^A I^B$.
Parent 1 genotype: $I^A I^B$
Parent 2 genotype: $I^A I^B$

The gametes produced by each parent will be $I^A$ and $I^B$.

From the Punnett square, the possible genotypes are:

• $I^A I^A$: Blood group A
• $I^A I^B$: Blood group AB
• $I^A I^B$: Blood group AB
• $I^B I^B$: Blood group B

Out of 4 possible offspring combinations, 2 have the genotype $I^A I^B$ (blood group AB).
Percentage of offspring with blood group AB = $\frac{2}{4} \times 100\% = 50\%$.

The correct option is C.

The final answer is $\boxed{\text{C}}$.