When copper turnings and concentrated $HCl$ are heated with copper sulphate,the compound formed is:

Which of the following is used for making railway tracks?

What are the impurities present in ruby and sapphire?

Which one of the following species is stable in aqueous solution?

Complete the following reactions:
$(a)$ $4FeCr_2O_4 + 8Na_2CO_3 + 7O_2 \to 8Na_2CrO_4 + 2Fe_2O_3 + 8CO_2$
$(b)$ $2Na_2CrO_4 + 2H^+ \to Na_2Cr_2O_7 + 2Na^+ + H_2O$
Identify the species $X$ in both reactions.

In ruby and emerald,the metal ion$(s)$ present is/are