2C(s)+O2(g)⟶2CO(g)Use the following reaction enthalpies to find the enthalpy of the first reaction. C(s)+O2(g)2CO2(g)→CO2(g)→2CO(g)+O2( g)ΔHΔH=−394 kJ=+28

1 a

2 d

3 a

4 c

explanation:

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.