Answer:
A
Explanation:
To label an element correctly using a combination of the symbol, mass number and atomic number furnishes some important information about the element.
We can obtain these information from the element provided that correct labeling of the element is presented. Firstly, after writing the symbol of the element, the atomic number is placed as a subscript on the left while the mass number of the atomic mass is placed as a superscript on the same left.
Looking at the question asked, we have the element symbol in the correct position as Ca, with 42 also in the correct position which is the mass number. The third number which is 20 is thus the atomic number of the element.
Silver and lead are special elements, where silver is insoluble in all halogen anions (like AgCl, AgI, AgBr)
and lead is insoluble in sulphates and halogen anions ( PbSO4, PbCl2, etc.)
Mercury is special because it is the only metal that is a liquid at room temperature
hope this helps!!
A temperature change in a reaction indicates a chemical change
