Explain the role of carbon in mole calculation and definition

What is the percentage composition of carbon in the compound ch4

Find the number of grams of hcl needed to react completely with .50 moles of magnesium.

100 grams of molten lead (600°c) is used to make musket balls. if the lead shot is allowed to cool to room temperature (21°c), what is the change in entropy (in j/k) of the lead? (for the specific heat of molten and solid lead use 1.29 j/g⋅°c; the latent heat of fusion and the melting point of lead are 2.45 × 104 j/kg and 327°c, respectively.)