Answer : The final number of moles of gas that withdrawn from the tank to lower the pressure of the gas must be, 0.301 mol.
Explanation :
As we know that:

At constant volume and temperature of gas, the pressure will be directly proportional to the number of moles of gas.
The relation between  pressure and number of moles of gas will be:

where,
 = initial pressure of gas = 24.5 atm
 = initial pressure of gas = 24.5 atm
 = final pressure of gas = 5.30 atm
 = final pressure of gas = 5.30 atm
 = initial number of moles of gas = 1.40 moles
 = initial number of moles of gas = 1.40 moles
 = final number of moles of gas = ?
 = final number of moles of gas = ?
Now put all the given values in the above expression, we get:


Therefore, the final number of moles of gas that withdrawn from the tank to lower the pressure of the gas must be, 0.301 mol.
 
        
             
        
        
        
Answer:
D) 5.15
Explanation:
Step 1: Write the equation for the dissociation of HCN
HCN(aq) ⇄ H⁺(aq) + CN⁻(aq)
Step 2: Calculate [H⁺] at equilibrium
The percent of ionization (α%) is equal to the concentration of one ion at the equilibrium divided by the initial concentration of the acid times 100%.
α% = [H⁺]eq / [HCN]₀ × 100%
[H⁺]eq = α%/100% × [HCN]₀
[H⁺]eq = 0.0070%/100% × 0.10 M
[H⁺]eq = 7.0 × 10⁻⁶ M
Step 3: Calculate the pH
pH = -log [H⁺] = -log 7.0 × 10⁻⁶ = 5.15
 
        
             
        
        
        
Its an inelastic collision because the force from the bat causes it to bounce back.  It is also an elastic force because catching the ball call for the energy of the ball to be deformed and restored into the mitt.