How many statements among the following is/are correct ? 1) C-C bond length in diamond is 154 pm. 2) Fullerene (C60) is aromatic. 3) Fullerene contains 20 six membered and 15 five membered ring. 4) H2CO3/HCO3 buffer system helps to maintain pH of blood between 7.26 to 7.42 5) Quartz is extensively used as piezoelectric material. 6) Hydrated zeolites are used as ion exchange in softening of hard water.