Abbreviation. DNA, which stands for deoxyribonucleic acid, is defined as a nucleic acid that contains the genetic code.
KE = (1/2)(m)(v^2)
KE = (1/2)(7)(4^2)
KE = (1/2)(112)
KE = 56 J
The given reaction is,

In this reaction, the positive and negative ions of both the reactants rearrange resulting in the formation of new compounds. Such a reaction is referred to as the double replacement or the double displacement reaction. These type of reactions usually take place in aqueous medium and one of the products is a precipitate.
Double displacement reactions are of three types, precipitation reaction, neutralization reaction and reaction involving the formation of a gas. The given reaction is a precipitation reaction as one of the products is a solid.
The milk curdling is a precipitate