In an experiment ,dry hydrogen gas was passed over hot copper (II) oxide in a combustion tube as shown in the diagram below ​

by upward delivery             the gas collected at the end is hydrogen and hydrogen is lighter than air that is why we use the upward delivery or you can also say the downwards displacement of air                                                  [b] hydrogen +copper[ii]oxide⇒water+copper                                                                                  

under a microscope, cancer cells may look very different from normal cells. they often have different sizes and some may be larger than normal while others are smaller. cancer cells are often abnormally shaped and the control centre of the cell (the nucleus) may have an abnormal appearance.

i think? ?