Einstein's equations showed that matter could be converted into energy; and vice-versa
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The correct choice is
B. Double-replacement reactions
in this type of reaction , two ionic compounds react and swaps their cations or anions giving two new compounds in the product. hence the double replacement reactions does not deal with the nucleus. all other terms like strong nuclear forces, radioactivity and nuclear decay deal with the nucleus.
A magnet contains billions of aligned atoms known as magnetic domains