White blood cells work in two ways; they can ingest or engulf pathogens and destroy them by digesting them. White blood cells can also produce antibodies to destroy particular pathogens by clumping them together and destroying them. They also produce antitoxins that counteract the toxins released by pathogens.
According to the second order formula:
1/[At] = K t + 1/[Ao]
and when we have the K constant =0.0265 & we have t = 180 min & we have the initial concentration of A = 4.25 so by substitution:
1/[At] = 0.0265 X 180min + 1/4.25
1/[At] = 5
∴[At] = 1/5 = 0.2 m
Answer: A. -396 kJ
Explanation:
The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states.
Reversing the reaction, changes the sign of 
On multiplying the reaction by 2, enthalpy gets multiplied by 2:
Thus the enthalpy change for the reaction is -396 kJ.
Ionic bond is a type of bond in which one or more atoms are transferred to another atom which results to two ions with opposite charge. They attract each other.
The atom of another element is removed and then gained by another element which produces a noble gas electron configuration.
Covalent bond is a type of bond in which a pair or more electrons are being shared by the atoms of two elements.
Because of this, the molecules become stable by sharing the electrons thus creating a noble gas configuration for each of the atom.
