How many types of genotypes are produced in the $F_2$ generation obtained from a dihybrid self-cross?

In Mendel's dihybrid cross,how many types of offspring were obtained in the $F_2$ generation that were different from the parental types?

In Mendel's pea plants,round seeds $(RR)$ are dominant over wrinkled seeds $(rr)$,and yellow cotyledons $(YY)$ are dominant over green cotyledons $(yy)$. What will be the phenotypic ratio in the $F_2$ generation of a cross between $RRYY$ and $rryy$?

In a plant with genotype $RrYy$,if self-pollination occurs,what will be the ratio of the following genotypes: $RRYY, RrYY, RRYy, RrYy$?

Which one of the following crosses will have a $1:1:1:1$ ratio of progeny?

Which law did Mendel propose based on the inheritance of two traits?