Fill in the blanks:
$(1)$ Cement is also known as......
$(2)$ Cement was first introduced by......

Bone ash contains

$MgO$ is used for lining furnaces because

The highest occupied energy level of the group $2$ elements is $7s^2$. Which of these statements is likely to be incorrect?

Which of the following ions has the largest heat of hydration?

Assertion : Of the various chlorides of alkaline earth metals $BeCl_2$ is covalent in nature,whereas $MgCl_2$ and $CaCl_2$ are ionic compounds.
Reason : $Be$ is the first member of group $2$.