Wavelengths of light from a distant galaxy are found to be 0.58% longer than the corresponding wavelengths measured in a terrestrial laboratory.

A) Is the galaxy approaching or receding from the earth?

B) At what speed?

The discovery of gallium was significant as it confirmed Mendeleev’s predictions and showed the usefulness of his table.

Option First

Explanation:

In 1871, Mendeleev prepared a periodic table of all known elements to study their properties. While making the table, he left some places in the table for elements that were yet to be discovered. One of the elements was eka-aluminium.  

In 1875, a French scientist Paul Emile Francois Lecoq de Boisbaudran discovered a new element spectroscopically in the course of examining zinc blende. This newly discovered element showed the same properties as predicted by Mendeleev for the eka-aluminium with an atomic weight 69.  

Later, the specific gravity of the element was also found to be the same as predicted by Mendeleev i.e. 5.9. After this, Lepoq named the element as Gallium, which confirmed Mendeleev’s predictions and made his periodic table worthier.