In the hexaploid wheat (42 chromosomes), the haploid (n) and monoploid (x) number of chromosomes are:

The correct option is C n = 21 and x = 7
The monoploid (x) number is the number of chromosomes in a single set. Since the number of chromosomes in hexaploid wheat is 42, the monoploid number will be $\frac{42}{6}=7.$ The haploid (n) number is the number of chromosomes in a gamete. For hexaploid wheat, the gamete will be triploid. The haploid number of chromosomes $=7\times 3=21.$