Which element from the following possesses half-filled $d$-orbitals either in expected or in observed electronic configuration?

Arrange the acids $H_2SO_4$,$H_3PO_4$,and $HClO_3$ in the decreasing order of their acidic strength.

In known elements,the maximum number is of

Which of the following is the correct order of acidic strength for $Al_2O_3$,$SiO_2$,$P_2O_3$,and $SO_2$?

Red hot carbon will remove oxygen from the oxides $XO$ and $YO$ but not from $ZO$. $Y$ will remove oxygen from $XO$. Use this evidence to deduce the order of activity of the three metals $X, Y$ and $Z$ putting the most active first.

Given below are two statements:
Statement $I$: Chlorine can easily combine with oxygen to form oxides,and the product has a tendency to explode.
Statement $II$: Chemical reactivity of an element can be determined by its reaction with oxygen and halogens.
In the light of the above statements,choose the correct answer from the options given below.