Which element would have the most valence electrons and also be able to react with hydrogen?

What is the volume of the fluid in the graduated cylinder with accuracy and measured to the correct degree of precision? 41.2 ml 42.0 ml 41.23 ml 41.89 ml

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Large helium-filled balloons are used to lift scientific equipment to high altitudes. what is the pressure inside such a balloon if it starts out at sea level with a temperature of 10.0ºc and rises to an altitude where its volume is twenty times the original volume and its temperature is – 50.0ºc ?