Consider the following reactions :
Which of these reactions are possible ?

The flocculation value of HCl for arsenic sulphide sol.
is 30 m mol L^-1 If H₂SO₄ is used for the flocculatiopn of arsenic sulphide, the amount in grams, of H₂SO₄ in 250 ml required for the above purposed is ______.
(molecular mass of H₂SO₄ = 98 g/mol)

3 g of acetic acid is added to 250 mL of 0.1 M HCL and the solution made up to 500 mL. To 20 mL of this solutions $${1 \over 2}$$ mL of 5 M NaOH is added. The pH of the solution is __________.

[Given : pKa of acetic acid = 4.75, molar mass of acetic of acid = 60 g/mol, log 3 = 0.4771] Neglect any changes in volume.

The standard heat of formation $$\left( {{\Delta _f}H_{298}^0} \right)$$ of ethane (in kj/mol), if the heat of combustion of ethane, hydrogen and graphite are - 1560, -393.5 and -286 Kj/mol, respectively is :