Increasing of atomic number in the same group cause .............................

Sodium oxide is from ......................................... oxides.

The first vertebrates that appeared are .......................................

The elements of group (7A) are called ...................................

In the periodic table, the elements which are identical in properties lie in the same ..........

The hottest atmospheric layer is ..................................

From the endangered species is ....................................

............................................... is from microfossils.

All the following are greenhouse gases, except ........................................

There are .................................. bond between water molecules.

When sodium reacts with water ............................. gas is evolved.