This question is about some compounds of the elements in Group 4 of the Periodic Table.(a) When carbon dioxide dissolves in water, a weak acid forms.(i) Which of these could be the pH of this weak acid? (1)A 1B 5C 7D 9(ii) Which of these is a correct statement about acids? (1)A acids contain OH −ionsB acids are electron donorsC acids are proton acceptorsD acids are proton donors(b) When lead(II) carbonate is heated, lead(II) oxide and carbon dioxide form.(i) Give the name of this type of reaction. (1) ....................................................................................................................................................................................................................................................................................(ii) Complete the equation for this reaction. (1) PbCO3 → .............................................. + ..............................................

(a) (i) The pH of this weak acid could be B 5. The pH scale ranges from 0 to 14, with 7 being neutral. Acids have a pH less than 7, but a weak acid would not be at the extreme end of the scale, so 5 is a reasonable estimate.

(ii) The correct statement about acids is D: acids are proton donors. This is based on the Brønsted-Lowry definition of acids and bases, where an acid is a substance that can donate a proton (H+ ion) and a base is a substance that can accept a proton.

(b) (i) The name of this type of reaction when lead(II) carbonate is heated to form lead(II) oxide and carbon dioxide is thermal decomposition. This is a type of reaction where one compound breaks down into two or more simpler substances when heated.

(ii) The completed equation for this reaction is: PbCO3 → PbO + CO2. This shows that one molecule of lead(II) carbonate (PbCO3) decomposes to form one molecule of lead(II) oxide (PbO) and one molecule of carbon dioxide (CO2) when heated.