what is the main difference between base pairing during DNA replication and base pairing during transcription

Replication involves DNA pairing with DNA, but transcription involves DNA pairing with RNA.

Replication means copying, and it applies to DNA. The two strands in a molecule of DNA separate, and a new strand of DNA is built (synthesized) along each, using the base-pairing rules: A (adenine) with T (thymine); C (cytosine) with G (guanine).

Transcription means the synthesis of a molecule of RNA along with one of the strands of DNA. The base-pairing rules are essentially the same, but RNA has no thymine (T): it has uracil (U) instead. So the base-pairing rules for transcription are (putting DNA first): A with U; C with G; G with C; T with A.

Explanation:

relative dating involves things like higher layers are most recent than rocks lower in the sequence. this can be extended to the known sequence of fossils. rocks containing rabbit fossils are later than those containing dinosaur fossils.  

absolute dating methods mainly use radioactive elements that have known rates of decay and produce recognizable products. for example potassium 40 decays to produce argon. once a rock has solidified the argon is trapped. by measuring the argon and potassium0 you can get an accurate number for the age.  

some other methods are good for archaeological ages. dendrochronology involves recognizing the sequence of tree rings. the orientation of magnetized particles in baked clay can be used to date a fire.

hope this .. .

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added