Which transition element of the $3d$ series is used in a dry battery cell?

$Fe(OH)_2$ is precipitated from $Fe(II)$ solutions as a white solid but turns dark green and then brown due to the formation of:

Presence of $Cr$ in steel makes it

In a borax bead test under hot condition,a metal salt is heated at point $B$ of the flame,resulting in a green-coloured salt bead. The spin-only magnetic moment value of the salt is $..........$ $BM$ (Nearest integer). [Given atomic number of $Cu=29, Ni=28, Mn=25, Fe=26$]

Which metal oxide is used to make blue glass?

Choose the correct statements from the following:
$A$. $Mn_2O_7$ is an oil at room temperature.
$B$. $V_2O_4$ reacts with acid to give $VO^{2+}$ ions.
$C$. $CrO$ is a basic oxide.
$D$. $V_2O_5$ does not react with acid.
Choose the correct answer from the options given below: