Example of intergenic gene interaction is/are

Mother and father both have blood group '$A$'. They have two children,one with blood group '$O$' and the second one with blood group '$A$'. They have:

Hybrid vigour is due to

What is the number of chromosome pairs in maize $(Zea \ mays)$?

In a plant,three dominant genes $A$,$B$,and $C$ must be expressed together to produce purple flowers. If any one or all three genes are in the recessive state,the flowers become colorless.
Raw material $\xrightarrow{A} X \xrightarrow{B} Y \xrightarrow{C} Z$ (Pigment)
$A$ purple-flowered plant with genotype $AABBCC$ is crossed with a colorless plant with genotype $aabbcc$. This results in $F_1$ hybrid purple offspring. What will be the proportion of purple-flowered plants in the $F_2$ generation produced by selfing the $F_1$ generation?

Which of the following statements are false?
$I.$ $A$ dominant allele determines the phenotype when paired with a recessive allele.
$II.$ $A$ recessive allele is weaker than a dominant allele.
$III.$ $A$ recessive allele does not show its effects when paired with a dominant allele.
$IV.$ $A$ dominant allele is always better for an organism.