Modern Frigates

A modern frigate is a ship that protects other ships, including military and merchant marine vessels. Anti-submarine escort vessels are included in the category of "frigate". The La Fayette class built by DCNS is a popular class of frigate used in the French Navy ("Marine Nationale") and those of other nations too.

When NOT to use Yours Sincerely

Yours faithfully and yours truly are the British and American equivalents used when signing off a letter to a recipient whose name you do not know.

Yours sincerely or Sincerely yours are used when you DO know the name of the recipient.

Mary Poppins' The Perfect Nanny is an example of how NOT to use Yours sincerely:

"Hurry nanny, Many thanks
Sincerely, Jane and Michael Banks".

Halogens and Diatomic Molecules in Swimming Pools

The halogens are a group in the periodic table consisting of the five related elements of fluorine, chlorine, bromine, iodine and astatine. It's also known as Group 7.

Group 1 elements react with Group 7 elements to form, for example, lithium bromide.

Halogens all exist as diatomic molecules, so Chlorine exists as Cl2, Fluorine similarly, two halogen atoms joined by a covalent bond (where electrons are shared between atoms).