if an element has a half-life of 30 million years and there is 12.5% of it remaining in a rock, how old is that rock

The half-life of a substance is the amount of time it takes for half of that substance to decay. However, after two half-lives, half of the half remaining will decay, leaving you with one quarter of the original substance.

So, after 1 million years you will have 50% of the original substance remaining.

And, after 2 million years you will have 25% of the original substance remaining.

After 3 million years you will have 12.5% of the original substance remaining.

And after 4 million years you will have 6.25% of the original substance remaining.

Explanation:

Hope it helps:)

water is a polar molecule. a chemical bond is a force of attraction between atoms or ions. bonds form when atoms share or transfer valence electrons. atoms form chemical bonds to achieve a full outer energy level, which is the most stable arrangement of electrons. so, false

explanation:

in h2o molecule, two water molecules are bonded by a hydrogen bond but the bond between two h - o bonds within a water molecule are covalent. the greater the electronegativity difference, the more ionic the bond is. bonds that are partly ionic are called polar covalent bonds. nonpolar covalent bonds, with equal sharing of the bond electrons, arise when the electronegativities of the two atoms are equal.

that would be called plucking : )

explanation:

''plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the erosion and transportation of individual pieces of bedrock, especially large "joint blocks". as a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock."