The graph below shows the radioactive decay of a material.

The graph shows 'Time in billion years' on the x axis and 'Percent of original mass remaining' on y axis. On the x axis the points 0, 2, 4, 6, and 8 are marked. On the y axis points 25%, 50%, 75%, and 100% are marked. A smooth curve joins the points (0, 100%), (2, 25%), (4, 12.5%), (6, 6.25%), (8, 3.125%).

If the original mass of the radioactive material was 500 grams, after how many billion years will its mass become 125 grams?

2 billion years
4 billion years
6 billion years
8 billion years

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protocol for imps extraction focusing on membrane protein extraction, solubilisation, and purification.

interphase

the period of cell growth when the cell synthesizes new molecules and organelles. the cell is not dividing and it constitutes the majority of the time spent in the cell cycle

prophase

changes occur in the nucleus and cytoplasm. the chromatin condenses to form structures (sister chromatids) visible with a light microscope and the mitotic spindle begins to form, but the nucleus is still in tact

prometaphase

the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the sister chromatids

metaphase

all the cell's duplicated chromosomes are lined up at an imaginary plane equidistant between the poles of the mitotic spindle

anaphase

begins when sister chromatids separate from each other and ending when a complete set of daughter chromosomes arrives at each of the two poles of the cell

telophase

the daughter nuclei form at the two poles of a cell

cytokinesis

the division of a cytoplasm to form two separate daughter cells. usually occurs during telophase during mitosis. this and mitosis make up to mitotic (m) phase of the cell cycle