Final answer:Helium is used to make balloons float because it is less dense than air and safer than hydrogen, which is highly flammable.Explanation:The period 1 element used to make balloons float is helium. This is because helium has a molar mass that is much less dense than air, allowing it to lift balloons above the ground. Unlike hydrogen, which is also less dense than air and was once used for airships such as the Hindenburg, helium is nonflammable and much safer to use. In addition, helium is historically significant as it was discovered due to a yellow emission line in the chromospheric spectrum that did not match any known elements at the time, leading to its naming after helios, the Greek word for 'Sun'....

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