You have the equations:

2H2O(l)→2H2(g)+O2(g), △H=572 kJ

2N2(g)+3H2(g)→2NH3(g), △H=−138 kJ
2NO2(g)+7H2(g)→2NH3(g)+4H2O(l), △H=−1.18×103 kJ 2NO2(g)→2N2(g)+2O2(g), △H=□

What is the missing △H ?

−1.38×103 kJ
+99.0 kJ
+1.38 × 10³ kJ
−138 kJ

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explanation:

because it is

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.