Drosophila melanogaster has $8$ chromosomes in its somatic cell. How many linkage groups will it have?

Which of the following is true about linkage?
$I.$ It is a phenomenon in which more recombinants are produced in $F_{2}$-generation.
$II.$ More parental combinations are produced in $F_{2}$-generation.
$III.$ Genotypes which are present in $F_{1}$ hybrid reappear in high frequency in $F_{2}$-generation.
$IV.$ It is a phenomenon in which two chromosomes are linked.

Which one of the following pairs is correctly matched?

The chromosome maps are not accurate maps because

The experiment shown in the given figure has been carried out by Morgan to show the phenomenon of linkage and recombination. If in cross $I$,genes are tightly linked and in cross $II$,genes are loosely linked,then what will be the percentage of recombinants produced in cross $I$ and cross $II$ respectively?

$A$: Crossing over is the exchange of genetic material between non-homologous chromosomes.
$R$: It produces new linkages.