11. why is the first ionization energy of a nonmetal much higher than that of an alkali metal in its same period

Well, nonmetals have more filled shells, making it harder to remove electrons, AND nonmetals have smaller atoms, while metals have larger atoms and therefore less attraction of the electrons to the nucleus. The nuclear charge increases from left to right across a period and the shielding effect stays the same. So it is more difficult to remove an electron from a nonmetal than an alkali metal. ;3

The density of water is 1 g/cm cubed and in order for the pebble to sink its density has to be greater than the density of water and in order for the twig to float its density has to be less than the density of water