Grass planting, laying of straw , putting up sediment fenced or knee high black fabric fences can help reduce no point source water pollution
All other elements react with other elements to form compounds. In the special case where the reaction produces fixed numbers of the same types of atoms in exactly the same configuration, we say the elements have formed a molecule.
The wavelength is the distance between one crest/trough to another crest/trough. On the image, it's basically the length between each peak of the wave. You can see that the distance between peaks in wave A are much shorter than the distance between the peaks in wave B.
Thus, wave B has the longer wavelength.
1 elements
2 they have same number of valence electrons
3 period