Answer: Elements in Group 2
Explanation: The periodic table was arranged by Dmitri Mendeleev specifically around similarites in their chemical behaviors. He found that as atomic number increases, at some point an element starts to react in a manner similar to a previous one. When that happened, he would place the larger element under the smaller one, and eventually noticed a periodicity in the table. Elements in a column (Groups) had similiar chemical properties. We know today that these similarities are due to the electron configuration, and that these configurations repeat themselves. He left gaps in the table when he could find an existing element with properties similar to others in that group. I big leap of faith, but it worked. Elements for those missing boxes were eventually discovered.
Answer:
Option A
Explanation:
Temperature of a body is due to the heat gained or loss. During a phase change, the atoms or molecules of a substance are undergoing change is temperature due to which no temperature change is observed during phase change. The heat in the transition phase is used to break bonds and the change in temperature is felt when kinetic energy change is complete. During transition, the average kinetic energy of the molecules remains unchanged and hence during a phase change a temperature do not changes until unless the phase change is completed.
Hence, option A is correct
Se - 78
Selenium - 78
or
78/34 Se2-
