What is the oxidation state of osmium in $7B$ and $7C$,respectively?

Metre scales are made up of which alloy?

When borax is heated with cobalt oxide,which of the following compounds produces a blue-colored bead?

Consider the following chemical reactions involved in the extraction of chromium from chromite ore:
$(a)$ $4FeCr_2O_4 + X_1 + 7O_2 \to 8Na_2CrO_4 + 2Fe_2O_3 + 8CO_2$
$(b)$ $2Na_2CrO_4 + X_2 \to Na_2Cr_2O_7 + 2Na^+ + H_2O$
Identify the species $X_1$ and $X_2$ in the reactions.

$ZnO \cdot CoO$ is called

Write about the oxides and oxoanions of transition metals.