I need some help please, I can't understand how to solve these problems? Write a balanced equation for the reaction:

4Fe + 3O2 ->2Fe2O3 (this is the equation in case it is necessary)

1. If an ordinary iron nail (assumed to be pure iron) has a mass of 2.68 g, what mass of Fe2O3, in grams, is produced if the nail is completely converted to the oxide?

2.What mass of O2, in grams, is required for the reaction?

please help.

the correct answer is b. a strong acid completely dissociates to its ions when dissolved in water. completely dissociates to and ions. a is incorrect because does not fully ionize to and ions and some remain as the compound . c and d are incorrect because, and do not fall into the category of bronsted lowry acids. a bronsted lowry acid is a proton donor and since both molecules do not have a proton to donate they are not bronsted lowry acids. likewise,   if we use the lewis acid definition, they cannot be acids. a lewis acid is an electron pair acceptor. both and have a complete octet so can not accept any electrons which disqualifies them as acids.

colorless gas, exhibiting a blue glow when placed in an electric field

b) solid

its a type of rock

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.