Answer:
Discovery of neutron
Explanation:
Until 1932, the atom was believed to be composed of a positively charged nucleus surrounded by negatively charged electrons, after successful discovery of electron by J.J. Thompson and proton by Ernest Rutherford.
In 1932, James Chadwick bombarded beryllium atoms with alpha particles.
As Chadwick had previously seen in experiment conducted by Frédéric and Irène Joliot-Curie, they had bombarded a sample of beryllium with alpha radiation.
Chadwick repeated the experiment and observed an unknown radiation, this showed no deflection what-so-ever.
He repeated this experiment by bombarding other materials, like helium, nitrogen and lithium,
Finally, Chadwick found that this radiation was composed of particles with a neutral electrical charge and had approximate mass of a proton.
This particle was then known as the neutron.
Answer:
In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
1. B. Calcium is a chemical element that can be found as Ca on the periodic table.
2 A. Heterogeneous mixture. Pizza is not uniform and is a variation of cheese, bread, and toppings that aren't mixed completely together.
3. B. Carbon Monoxide, or CO, is a chemical compound, a combination of 2 or more chemical elements.