An open-ended mercury manometer is used to measure the pressure exerted by a trapped gas as shown in figure. Initially manometer shows no difference in mercury level in both columns as shown in diagram. After sparking,  $\text{'}A\text{'}$ dissociates according to the following reaction  ${\text{A}}_{\left(\text{g}\right)}\to {\text{B}}_{\left(\text{g}\right)}{\text{+3C}}_{\left(\text{g}\right)}$ If pressure of gas  $\text{'}A\text{'}$ decreases to  $0.\text{9 atm}$ then choose the correct statements. (Assume temperature is constant and it is  $\text{3}00\text{ K}.$)