For atoms in the periodic table, the given mass number is the sum of the number of the protons (also called the atomic number) and the number of the neutrons inside its nucleus. Mathematically,
mass number = atomic number + number of neutrons
Substituting,
39 = 19 + n
n = 39 - 19 = 20
Therefore, the answer is not found in the choices.
Explanation:
Water evaporates from the surface of the earth and through the leaves of the plants and trees by absorbing the heat energy from the surrounding.
This water then converts into vapour and goes up into the atmosphere where the temperature is low in the troposphere and condenses to form the clouds. During the cloud formation the heat form the vapour is absorbed in the troposphere.
These clouds when get saturated then fall in the form of precipitation of water, snow etc. Replenishing back the water of the earth.
The velocity of the ball and the man is 0.259 m/s
Explanation:
We can solve this problem by using the law of conservation of momentum. In fact, in an isolated system, the total momentum before and after the collision must be conserved. Therefore, for the ball-man system, we can write:
where:
is the mass of the ball
is the initial velocity of the ball
is the mass of the man
is the initial velocity of the man
is the final velocity of the man and the ball after the collision
Re-arranging the equation and substituting the values, we find the final velocity:

So, the man and the ball slides on the ice at 0.259 m/s.
Learn more about momentum:
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Answer:
The correct answer will be-
1. Dependent variable- The growth of plant in the form of height
2. Independent variable- different temperature
3. Constant variable- The amount of water, amount of sunlight, type of soil.
Explanation:
A Scientific experiment must include three types of variables which are: The independent, dependent and the constant variable.
1. Independent variable- The variable which can be modified or changed either on its own or manually. The variable directly influences the variable to be studied. In the given condition, the independent variable is the different temperature provided to the plants.
2. Dependent variable- The variable which is being studied in the experiment and directly influenced by the independent variable is the growth of the plant which is measured in the form of height.
3. Constant variable- The variable which is kept constant throughout the experiment and remains the same which could be the amount of water amount of sunlight and type of soil.