Answer: A) grinding coffee beans
Explanation:
A physical change is defined as a change in which there is alteration in shape, size etc. No new substance gets formed in these reactions.
A chemical change is defined as a change in which a change in chemical composition takes place. A new substance is formed in these reactions.
1. Grinding coffee : Only change in size takes place, thus a physical change
2. Baking a cake: the chemical reaction occurs by combination of flour with oxygen , thus a chemical change.
3.:converting water to hydrogen and oxygen: The decomposition iof water takes place, thus is a chemical change
4.Burning of coal: the chemical reaction occurs by combination of carbon with oxygen , thus a chemical change.
Answer: 
incorporates both ionic bonding and covalent bonding.
Explanation:
A covalent bond is formed when an element shares its valence electron with another element. This bond is formed between two non metals.
An ionic bond is formed when an element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element and the element which accepts the electrons is known as electronegative element. This bond is formed between a metal and an non-metal.
For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.
Here potassium is having an oxidation state of +1 called as 
cation and nitrate 
is an anion with oxidation state of -1. Thus they combine and their oxidation states are exchanged and written in simplest whole number ratios to give neutral .
is formed by sharing of electrons between two non metals nitrogen and oxygen.
Thus incorporates both ionic bonding and covalent bonding.
Recorded by a seismograph.
Answer:
6.61 Pounds
Solution:
Step 1: Calculate Mass of Water as;
Density = Mass ÷ Volume
Solving for Mass,
Mass = Density × Volume ------ (1)
As,
Density of Water = 1 g.cm⁻³
And,
3 L of Water = 3000 cm³
Putting values in equation 1,
Mass = 1 g.cm⁻³ × 3000 cm³
Mass = 3000 g
Step 2: Convert Grams into Pounds;
As,
1 Gram = 0.002204 Pounds
So,
3000 Grams = X Pounds
Solving for X,
X = (3000 Grams × 0.002204 Pounds) ÷ 1 Gram
X = 6.61 Pounds
