Na2SO3” represents sodium sulfite. What does the 4 mean in the formula 4Na2SO3?

There are four atoms of sodium.
There are four atoms of sodium sulfite.
There are four molecules of sodium sulfite.
There are four elements in sodium sulfite.
PLEASE HELP I ONLY HAVE 30MIN and i have a test today and i will be happy if you help me :)

Consider the particle-in-a-box problem in 1d. a particle with mass m is confined to move freely between two hard walls situated at x = 0 and x = l. the potential energy function is given as (a) describe the boundary conditions that must be satisfied by the wavefunctions ψ(x) (such as energy eigenfunctions). (b) solve the schr¨odinger’s equation and by using the boundary conditions of part (a) find all energy eigenfunctions, ψn(x), and the corresponding energies, en. (c) what are the allowed values of the quantum number n above? how did you decide on that? (d) what is the de broglie wavelength for the ground state? (e) sketch a plot of the lowest 3 levels’ wavefunctions (ψn(x) vs x). don’t forget to mark the positions of the walls on the graphs. (f) in a transition between the energy levels above, which transition produces the longest wavelength λ for the emitted photon? what is the corresponding wavele

Which configuration would produce an electric current? a) rotate a coil of copper wire between two magnets. b) connect a wire between a copper and zinc strip sitting in a beaker of water. c) connect a wire to the (+) positive end of a battery and the other end to a light bulb. d) connect a wire to the negative end of a battery and the other end to a light bulb.

It is reasonable to assume that the bulk modulus of blood is about the same as that of water (2.2 gpa). as one goes deeper and deeper in the ocean, the pressure increases by 10000 pa for every meter below the surface. if a diver goes down 80.0 m in the ocean, by how much does each cubic centimeter of her blood change in volume? give the answer in cubic centimeters (actually one cubic centimeter equals one milliliter).