Kimchi is one of the traditional foods in China.

(1) In this study, if a jar is used, the conclusion may be accidental. Taking three cans for the same treatment can reduce the error and make the conclusion more reliable.

(2) The abscissa is time and the ordinate is nitrite content. The data in the comparison table are drawn and then connected with smooth curves.

(3) According to the data and figures in the table, we can see that the content of nitrite in pickle jars is different in different periods. ② On the 4th day after curing, the content of nitrite reached the peak; ③ On the first day of curing 12, nitrite reached the lowest value and remained basically unchanged; ④ The content of nitrite in pickled vegetables remained unchanged after heating and cooking.

(4) In the design of this study, the three jars were compared before and after boiling, and there was no control experiment to stop boiling after adding boiled salt solution, so there was an obvious defect in this study: there was no control, that is, 1 pickle jar with the same size as the first three jars was needed, and the boiled NaCl solution with the mass fraction of 10% was filled in it; If there is a water seal, it should also be tested at the same time with the above test group.

So the answer is:

(1) Reduce the error and make the conclusion more reliable; ( 1)

(2) You can draw one picture or three pictures respectively (3 points), and each altar trend is given 1 point respectively)

(3)① The content of nitrite in pickle jars is different in different periods; ② On the 4th day after curing, the content of nitrite reached the peak; ③ On the first day of curing 12, nitrite reached the lowest value and remained basically unchanged; (4) After the pickled vegetables are heated and cooked, the nitrite content remains unchanged. (2 points, 2 points for 1 point, not 0.5 point)

(4) There is an obvious defect in the design of this study: there is no comparison, that is, 1 pickle jar with the same size as the first three jars needs to be filled with boiling NaCl solution with the mass fraction of 10%( 1 min); And water seal, should also be tested at the same time with the above test group. (1 min)