Sodium benzoate is a bitter chemical often used in tiny amounts as a food preservative. the ability of humans to taste sodium benzoate is caused by a dominant allele, t. the recessive allele ("non-taster") is n. what are the genotypes of a "taster" and what are the genotypes of a "non-taster"?

If the dominant allele is t and the recessive allele ("non-taster") is n, than tn and tt are the  genotypes of a "taster". tn is heterozygous and tt is dominant homozygous. nn is the genotype of a "non-taster" and it is recessive homozygous.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added