Which of the following disorders exhibits sex chromosomal monosomy?

Match Column $I$ with Column $II$ and find the correct answer.

Column $I$	Column $II$
$(A)$ Aneuploidy	$(i)$ Increase in whole set of chromosomes
$(B)$ Monoploidy	$(ii)$ Loss or gain of a chromosome
$(C)$ Polyploidy	$(iii)$ Two sets of chromosomes
$(D)$ Diploidy	$(iv)$ $A$ single set of chromosomes

Frequency of Down's syndrome increases when the maternal age is

The number of chromosomes in Down's syndrome is

Given below are two statements :
Statement $I$ : Down's syndrome is caused by the absence of one of the $X$-chromosomes.
Statement $II$ : Turner's syndrome is caused by the presence of an additional copy of the chromosomes.
In the light of the above statements, choose the correct answer from the options given below :

Who reported that Down's syndrome is due to an extra $21^{st}$ chromosome?