10) D
Let ‘T’ be the dominant allele and let ‘t’ be the recessive allele.
T t
T TT Tt
t Tt tt
We know that recessive allele prevents seed development, which is why all seeds which had ‘tt'(1/4×1000 = 250) are dead. The remaining 750 seeds developed.
Out of these 750 seeds, some have ‘TT’ whilst others have ‘Tt’
From the table, we can see that 2 out of three plants are Tt whilst 1/3 are TT.
Number of heterozygous plants in the 750 mature plants = 2/3 = 66.666..% ≈ 67%