Polyphosphates are used as water softening agents because they

Lead is present in maximum quantity in which of the following types of glass?

Which one of the following elements reacts with steam?

$Si_2O_7^{6-}$ anion is obtained when

Identify the correct statement$(s)$ from the following: $I$. The catenation property of group $14$ elements decreases from carbon to tin. $II$. Fullerene $(C_{60})$ has $20$ five-membered carbon rings and $12$ six-membered carbon rings. $III$. $SiO_2$ is soluble in conc. $NaOH$.

Two statements are given below.
Statement $I$: $SnF_4$ and $PbF_4$ are ionic in nature.
Statement $II$: $GeCl_2$ is more stable than $GeCl_4$.
The correct answer is: