Which of the following substances will react with concentrated $H_2SO_4$?

Fill in the blanks:
$(1)$ ......... method is used to prepare sodium carbonate.
$(2)$ Sodium carbonate exists as .........
$(3)$ Sodium chloride is commonly known as .........
$(4)$ Sodium chloride melts at ......... temperature.

What is the chemical formula for calcium cyanamide?

Which alkali metal carbonate decomposes on heating to liberate $CO_2$ gas?

Which of the following metal carbides is known as a methanide?

The correct variation of the following properties of group $1$ elements $(M)$ ($Li$ to $Cs$) is: