One success of johann döbereiner's law of triads was that it organized most of the known elements into three-element groups based on similarities in their properties. (points : 2)
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True.

Explanation:

In 1824, the German chemist Johann Dobereiner, when analyzing the chemical elements calcium (Ca), strontium (Sr) and barium (Ba), noticed a simple relationship between their atomic masses: the mass of the strontium atom was very close to mass average of the other two elements. This observation was named the Triads of Chemical Elements and thus was born the law of the triads of Johann Döbereiner.

This law argued that elements with similar properties, ie, which reacted similarly with other elements, were organized in groups of three.

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2

answer carbon and three oxygen atoms;