When helium was discovered by humans?

Great amounts of electromagnetic energy from our sun and other bodies in space travel through space. which is a logical conclusion about these electromagnetic waves? their energy must be very their frequency must be very low these waves can travel without a medium they only travel through a vacuum of space

Write the chemical formula for a compound that is made of an element from group 1 and an element from group 17

Use the periodic table to find the molar mass of each element. molar mass h = g/mol molar mass s = g/mol molar mass o = g/mol