Which of the following metals will react with water?

When a metal of group $1$ was dissolved in liquid ammonia,the following observations were obtained :
$(a)$ Blue solution was obtained initially.
$(b)$ On concentrating the solution,the blue colour changed to bronze colour.
How do you account for the blue colour of the solution? Give the name of the product formed on keeping the solution for some time.

Identify the basic oxide from the following.

Anhydrous $Na_2CO_3$ is also known as:

Which one of the following is an $s$-block element?

Which of the following combinations will produce $H_2$ gas?