(2) The simplest way to judge whether well water is hard water is to add soapy water to the water. If there are many scum, well water is hard water; if there are many foams, well water is soft water.
(3) There are many ways to save water in daily life, such as washing rice, watering flowers, mopping the floor with bath water, and turning off the tap after using your hands. Raising the water price in Beijing can not only make up for the lack of funds of tap water production enterprises, but also stimulate people's awareness of water saving through price leverage;
(4)① As can be seen from the figure, the gas volume of the injector connected with A is large, and the gas volume of the injector connected with B is small, so it can be inferred that A is the negative electrode and B is the positive electrode;
(2) At first glance, all three 2)ABC terms meet the mass ratio of oxygen to hydrogen of 8: 1. At this time, we must not forget that the solute mass fraction of the solution was 10%. When a part of water is decomposed, the solvent decreases, that is, the total mass of the solution decreases, but the solute sodium hydroxide does not decrease, so the solute mass fraction in the final remaining solution will increase, so C is selected correctly.
So the answer is: (1) water is the source of life, and finding water means finding alien life;
(2)D；
(3) Washing rice and flushing toilets (or washing vegetables and watering flowers or not throwing garbage into the river) improve people's awareness of water saving (or reducing fresh water resources, polluting water bodies, increasing water consumption, etc.). );
④ ① positive, ② C.