What does green manure provide?

Which of the following statements is correct for $CsBr_3$?

Assertion $(A):$ Above Curie temperature, a ferromagnetic material becomes paramagnetic.

Reason $(R):$ When a magnetic material is heated to very high temperature, it loses its magnetic properties.

The coordination number of a metal crystallizing in a hexagonal close-packed structure is

Two uniform strings $A$ and $B$ made of steel are made to vibrate under the same tension. If the first overtone of $A$ is equal to the second overtone of $B$ and if the radius of $A$ is twice that of $B$,the ratio of the lengths of the strings is :

Sodium is heated in air at $300^{\circ} C$ to form $X$. $X$ absorbs $CO_2$ and forms $Na_2CO_3$ and $Y$. Which of the following is $Y$?