Which of the following statements correctly describes how mendel accounted for the observation that traits had disappeared in the f1 generation and then reappeared in the f2 generation?
(a) traits can be dominant or recessive, and the recessive traits were "hidden" by the dominant ones in the f1.
(b) new mutations were frequently generated in the f2 progeny, causing traits that had been lost in the f1 to reappear in the f2.
(c) members of the f1 generation had only one allele for each trait, but members of the f2 had two alleles for each trait.
(d) the mechanism controlling the appearance of traits was different between the f1 and the f2 plants.

Option A, Traits can be dominant or recessive, and the recessive traits were "hidden" by the dominant ones in the F1.

Explanation:

Mendel concluded from his study that traits can be of two types one dominant and the other one recessive.

A recessive trait is one which will only express phenotypically when there are two recessive alleles in pair.

hence, during F1 generation recessive traits were hidden by dominant  ones in the F1 to reappear in the F2 generation in the ration of 3:1

For example -

"R" represents allele for dominant red color of flower and "r" represents allele for recessive white color of flower.

Thus when two parents flower with homozygous genotype for both the traits is crossed, then following offspring are produced in the F1 generation -

RR * rr

Rr, Rr, Rr, Rr

Thus all progeny's are heterozygous red and white color disapears

but in F2 generation, two parents from F1 generations are crossed there by producing following offspring -

Rr * Rr

RR, Rr, Rr, rr

red: white

3:1

Hence, option A is correct.