Dna samples can be separated according to size using the technique of
(1) chromatography (3) replication
(2) electrophoresis (4) dissection

Option 2

Explanation:

Electrophoresis or in general known as "Gel electrophoresis" is a process by which separates and arranges DNA as per their size. In this process, DNA samples are placed at one end and at the other end electric current is applied. As we know that DNA fragments carry negative charge on them, hence they move towards the positively charged electrode. Also, all the DNA fragments have the same charge on it, therefore the larger the DNA fragment the more negatively charged the DNA is and hence the more rapidly it moves towards the positive electrode.  

At the end of the electrophoresis, same-sized DNA fragments arrange themselves in a row.  

Hence, option 2 is correct

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.