Answer:
The tension is 
Explanation:
From the question we are told that
The total mass is 
The radius is 
The density of air is 
Generally the upward force acting on the balloon is mathematically represented as

=> 
=> 
Here V is the volume of the spherical helium filled balloon which is mathematically represented as

=> 
=> 
So


1. Frequency: 
The energy given is the energy per mole of particles:

1 mole contains a number of Avogadro of particles,
, equal to
particles
So, by setting the following proportion, we can calculate the energy of a single photon:

This is the energy of a single photon; now we can calculate its frequency by using the formula:

where
is the Planck's constant
f is the photon frequency
Solving for f, we find

2. Wavelength: 
The wavelength of the photon is given by the equation:

where

is the speed of the photon (the speed of light). Substituting,

Answer:
When the object is placed at the focus the image is formed at infinity.
Explanation:
When a ray passes through focus and incident on a concave mirror then it will travel parallel to principal axis after reflection.Hence the image is formed at infinity.
This can be seen through the fact that Aksionov has the ability to seek his own justice many times throughout the story, yet does not take it