When the elements on the periodic table are arranged by increasing atomic numbers, the atomic mass generally increases as the atomic number increases. For some elements, however, the atomic mass of the element is lower than the atomic mass for the element that came before it. Explain how this could be possible.

no clue honey ima just get a life and go home

substitution is the answer in this case

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.