# Something Very Necessary

Here is another elementary REBUS for you to solve. As the Caption states, it is Something Very Necessary.

THIJKFELMNO

Be Fast ;)

TRUST. As @Lawrence has outlined, HIJKLMNO is H2O, also known as water, and FE is iron. These are chemical symbols, which fits the 'Elementary' hint.

When water interacts so intimately with iron, the iron corrodes to form RUST. Append that to the T in front and you get TRUST!

Why is that necessary? Because humans are social creatures, and without it, our most intimate relationships will corrode, just as the water corrodes the iron....

Apologies about the formatting! Am on my phone.

• Well done AZGreenTea. As for @Lawrence, He should have kept faith :P – Prashant Mar 17 '16 at 10:22

Tritium (T) in heavy water - said to be a "radiation hazard when ... ingested via ... water".
The letters T is on the outside, with FE interspersed among HIJKLMNO, i.e. H to O (H2O = water). Iron (Fe) with water could be considered heavy water. Heavy water normally contains deuterium, but tritium is hydrogen-3 is arguably even heavier.

It's elementary because

the answer relates to element symbols.

It's "very necessary" because

H2O (water) is necessary to ongoing life.

And "be fast" because

T is toxic. On the outside, T is not considered dangerous because "its beta particles are unable to penetrate the skin". Ingested via water, though, it's a radiation hazard.

• Spoiler alert please :P And it is not correct BTW, nor the previous two edits. :) – Prashant Mar 17 '16 at 8:42
• All you've got to do is remove the space between the two lines. – Prashant Mar 17 '16 at 8:49
• @Prashant Ha! You got it! – Lawrence Mar 17 '16 at 8:50
• Nope, but keep faith ! I like your thought-process though. – Prashant Mar 17 '16 at 9:28
• @Prashant I was in the middle of another bout of editing, but ran out of time (needed to do other things IRL). Good answer from AZGreenTea, and nice question! :) – Lawrence Mar 18 '16 at 2:24