Answer: 0.004 moles
Explanation:
Amount of substance= mass/ molar mass
Mass= 250mg or 0.25g
Molar mass= 58.44gmol-1
Amount= 0.25/58.44
= 0.004 moles
Any buffer exists in this equilibrium
HA <=>

In a buffer, there is a large reservoir of both the undissociated acid (HA) and its conjugate base (

)
When a strong acid is added, it reacts with the large reservoir of the conjugate base (

) forming a salt and water. Since this large reservoir of the conjugate base is used, the ph does not alter drastically, but instead resist the pH change.
Answer:
Three things about our body's systems:
All systems have a method of self-regulation or exogenous regulation by other systems.
All systems have a balance in their functions.
All the systems of our organism are intertwined with each other thus giving general vitality.
Explanation:
Best known systems:
Renal, respiratory, circulatory, cardiac, nervous, immune, blood, muscular systems.
All of them include the participation of one or more organs