Which among the following is non-poisonous in nature?

The basicity of orthophosphoric acid $(H_3PO_4)$ is:

Which element of group $15$ forms the most basic compound with hydrogen?

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 $\%$)?

In the following reaction,identify the nature of the product formed by the underlined atom upon complete hydrolysis at $R.T$.:
$H_4\underline{P}_2O_8 + H_2O \longrightarrow H_3PO_4 + H_2O_2$

$NH_3$ is $NOT$ used in which of the following?