Which of these is a pure substance?

a penny

sugar

ocean water

iced tea

Which of the following statements correctly describe nitrogen and its role as a plant nutrient? -Nitrogen is a macronutrient in plants. -Nitrogen-fixing bacteria in the soil convert N2 to NH3.

Explain why, in terms of the energy involved in bond breaking and bond making, the combustion of methane is exothermic.

Which describes a value for density?

The main source of energy that powers the earth is the A coat B electrical C moon D sun

When Dmitri Mendeleev published his periodic table of the elements in 1869, there were 59 known elements. Today there are 118 known elements.

How can a neutral atom become a positively-charged particle?

The last column of the periodic table contains the noble gases, elements that do not easily form chemical bonds.

When pollution is removed from the air by a natural process, it

What atomic property is different in each isotope of an element?

How do carbon-12 and carbon-13 differ? Select all that apply. They have different amounts of neutrons. They have different atomic charges. They have different mass numbers. They have different amounts of electrons.