Haber process is used for the production of which of the following?

In the brown ring test,the brown colour of the ring is due to

Which pair of metals does not dissolve in nitric acid?

How many of the following reactions will form $PH_3$ gas?
$(1)$ $Ca_3P_2 + H_2O \to$
$(2)$ $H_3PO_3 \xrightarrow{\Delta} $
$(3)$ $P_4 + NaOH \to$
$(4)$ $H_3PO_4 \xrightarrow{\Delta} $
$(5)$ $HNO_3 + P_4O_{10} \to$
$(6)$ $P_4 + HNO_3 \to$

Nitrogen combines with metals to form

Red phosphorus can be obtained from white phosphorus by: