George Eastman introduced roll film and the simple Kodak box camera in 1888. This was revolutionary for several reasons:

• Before Eastman's roll film, photography required heavy glass plates, complex chemical baths, and specialist knowledge — making it impractical for rapid journalistic work
• The Kodak camera was simple enough for anyone to use (“You press the button, we do the rest” was Eastman's slogan), democratising photography
• Roll film was lighter and easier to load than glass plates, making field photography faster and more mobile
• This, combined with the halftone process (1881) and smaller cameras like the 35mm Leica (first marketed 1925), created the conditions for modern photojournalism

The photojournalist tradition — using shocking or revealing images to change public opinion and drive legislation — was enabled directly by these technological advances.

Rewrite the expression to have a denominator that is a power of 10:

$\dfrac{1}{2^{11} \cdot 5^{17}} = \dfrac{1}{2^{11} \cdot 5^{17}} \times \dfrac{2^6}{2^6} = \dfrac{2^6}{2^{17} \cdot 5^{17}} = \dfrac{64}{10^{17}}$

So the decimal is $\dfrac{64}{10^{17}} = 0.\underbrace{00\ldots0}_{15}64$

The nonzero digits are $6$ and $4$ — that is, two nonzero digits.

Chloroxylenol contains a phenolic –OH group → Ferric chloride test (R). Norethindrone has a primary amine group → Carbylamine test (P). Sulphapyridine contains a C=C double bond (unsaturation) → Bayer's test (S). Penicillin is a carboxylic acid → Sodium hydrogencarbonate test (Q). So: $A \to R,\ B \to P,\ C \to S,\ D \to Q$.

Bilateral symmetry (also called axial or mirror symmetry) means one half of the composition is the mirror image of the other about a central axis.

Examples in architecture: Taj Mahal (bilateral symmetry on all four sides), most classical Greek temples, and many government buildings.

Other design principles: Rhythm = repetition of elements creating movement. Radial balance = elements arranged around a central point. Contrast = juxtaposition of opposing elements (light/dark, old/new).