Answer:
Mendeleev had left the noble gases out of his periodic table.
Explanation:
Mendeleev's periodic table is pictured in the image attached to the question.
Mendeleev's table obviously lacked the noble gases. The reason for this grave omission is simple; the noble gases were not known as at the time when he formulated his periodic table. There weren't any known elements whose properties were similar to the properties of the noble gases. This would have lead him to suspect their existence.
Based on the data given in this question, the statement that shows a correct interpretation of the chemical reactions is as follows: reaction A was exothermic and reaction B was endothermic.
<h3>What are endothermic and exothermic reactions?</h3>
Endothermic reaction is a chemical reaction that absorbs heat energy from its surroundings while exothermic reaction is a reaction that releases energy in the form of heat.
Endothermic reactions leave their surroundings cooler while exothermic reactions leave their surroundings hotter.
According to this question, the initial and final temperatures of two reactions are given as follows:
- Reaction A: 25.1°C and 30.2°C
- Reaction B: 25.1°C and 20.0°C
From the above data, reaction A was exothermic because it increased the surrounding temperature and reaction B was endothermic because it reduced the surrounding's temperature.
Learn more about endothermic and exothermic at: brainly.com/question/23184814
#SPJ1
