Disadvantages of Mendeleev's periodic table

Various limitations of Mendeleev's periodic table are:-

Position of hydrogen - he couldn't assign a correct position to hydrogen as it showed properties of both alkali and halogens .

Position of isotopes - he considered that the properties of elements are a function of their atomic masses. Hence isotopes of a same element couldn't be placed.

In the d-block , elements with lower atomic number were placed before higher atomic number.

Explanation:

the correct answer is option d

explanation:

i was wrong its d because they dont use cm when calculating square roots

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.