(1)① The valence of phosphorus in phosphorus pentoxide can be expressed as +5p2o5, in which the upper part of the element is represented by symbols and numbers, with the symbols in front and the numbers behind.

The most abundant metal element in the earth's crust is aluminum, and its symbol is al.

Carbon dioxide can make clear limewater turbid and is often used to test carbon dioxide. Carbon dioxide reacts with calcium hydroxide to produce calcium carbonate and water. The chemical equation of the reaction is CO2+Ca (OH) 2 ═ CaCO3 ↓+H2O.

② According to chemical equation 2Cu(NO3)2△. 2CuO+NO2。 ↑+4X↑, the atomic numbers of copper, nitrogen and oxygen in the reactant are 2, 4 and 12 respectively, and the atomic numbers of copper, nitrogen and oxygen in the product after the reaction are 2, 0 and 4 respectively. According to the kinds and numbers of atoms before and after the reaction, 4X contains four nitrogen atoms and eight oxygen atoms, so each X molecule is composed of 65438+.

(2) ① At t℃, the solubility curves of M and N intersect at one point, which means that at T℃, the solubility of M and N is equal.

② Solubility is not affected by temperature, and there is a small amount of M in N solution. Now, in order to extract pure nitrogen, evaporation and crystallization should be adopted.

③ Because the shaded part is above the solubility curve of M and below that of N, it is a saturated solution for M and an unsaturated solution for N. 。

The solubility of n increases with the increase of temperature, so the unsaturated solution of n can be transformed into saturated solution by evaporating solvent, adding the same solute and cooling down.

So the answer is: (1) ①+5p2o5; al； co2+ca(oh)2═caco3↓+h2o； ②NO2； (2) ① At T℃, the solubility of M and N is equal; ② Evaporation; ③N； C.