Select the salt whose aqueous solution is not green.

Given below are some statements about $Mn$ and $Mn_2O_7$. Identify the correct statements:
$A$. $Mn$ forms the oxide $Mn_2O_7$ in which $Mn$ is in its highest oxidation state.
$B$. Oxygen stabilizes the $Mn$ in higher oxidation states by forming multiple bonds with $Mn$.
$C$. $Mn_2O_7$ is an ionic oxide.
$D$. The structure of $Mn_2O_7$ consists of one bridged oxygen.
Choose the correct answer from the options given below:

Which alloy of steel is used in making automobile parts and utensils?

Which of the following compositions is found in dental amalgam alloys?

$A$ group of acidic oxides is

Identify the wrong statement regarding copper$(II)$ sulphate $(CuSO_4)$.