Difference in equation?

Ca+2HNO3 = H2+Ca(NO3)2
Can you tell me why is the 2 infront of 'HNO3' and the 2 behind 'H'. What is the difference, pls explain.

Which of the following aqueous solutions remains neutral after
electrolysis

In the reaction A + 2B ⇌ 2C, if 2 moles of A, 3 moles of B and 2 moles of C are placed in a 2 L flask and
the equilibrium concentration of C is 0.5 mol/L. The equilibrium constant (KC) for the reaction is.....and please tell how you know that the reaction is going forward .. imean how to calculate the reaction quotient ???

 

True or false when an electron in ground state of hydrogen atom is excited with an energy that is greayer than e2-e1 but less than e3-e1 the electron will get excited n=2

18 19 gram mixture of na2co3 and nahco3 on heating gives 2.2 gram CO2 gas find the percent nahco3 (by mass) in mixture

A 100 cm cube solution of sodium carbonate is prepared by dissolving 8.653 g of salt in water the density of solution is 1.0816g per ml what are the molarity and molality of the solution.