What is common for chlorine and bromine?

Analysis:

Chlorine (Cl) and Bromine (Br) are both halogens in Group 17 of the periodic table.

• 1) наличие на внешнем электронном слое одинакового числа электронов (having the same number of electrons in the outer electron shell): Both chlorine and bromine have 7 valence electrons. This is a common characteristic of halogens.
• 2) наличие четырёх электронных слоёв в атомах (having four electron shells in atoms): Chlorine has 3 electron shells, and bromine has 4 electron shells. So this is not common.
• 3) одинаковое физическое состояние образованных ими простых веществ (same physical state of the simple substances formed by them): At room temperature, chlorine is a gas, and bromine is a liquid. So this is not common.
• 4) образование ими высших оксидов с общей формулой R2O7 (formation of highest oxides with the general formula R2O7): Chlorine forms Cl2O7, and bromine forms Br2O7. This is a common characteristic.
• 5) то, что они являются более сильными окислителями, чем фтор (being stronger oxidizing agents than fluorine): Fluorine is the most electronegative and strongest oxidizing agent among halogens. Both chlorine and bromine are weaker oxidizing agents than fluorine.

Based on the analysis, options 1 and 4 are common characteristics.

Answer: 1, 4