Which of the following elements of group $15$ $(VA)$ does not show allotropy?

Excess of ammonia with sodium hypochlorite solution in the presence of glue or gelatine gives:

Amongst the following compounds:
$I.$ $H_5P_3O_{10}$
$II.$ $H_6P_4O_{13}$
$III.$ $H_5P_5O_{15}$
$IV.$ $H_7P_5O_{16}$
Which of these are non-cyclic phosphates?

What is the maximum concentration of aqueous $HNO_3$ that can be obtained by distillation with concentrated $H_2SO_4$ in terms of percentage by mass (in $\%$)?

Which of the following has the highest ratio of reducing hydrogen atoms to $OH$ groups?

An orange solid $(X)$ on heating,gives a colourless gas $(Y)$ and a green residue $(Z).$ Gas $(Y)$ on treatment with $Mg,$ produces a white solid substance. Identify the white solid substance.