Which of the following elements is a metalloid?

Which one is the strongest acid?

Choose the typical element.

In the following,the element with the highest electropositivity is

Three elements $X$,$Y$ and $Z$ are in the $3^{rd}$ period of the periodic table. The oxides of $X$,$Y$ and $Z$,respectively,are basic,amphoteric and acidic. The correct order of the atomic numbers of $X$,$Y$ and $Z$ is:

Explain the trends in physical and chemical reactivity of elements across a period and down a group.