Natal Mercury house is the sign where your Mercury was placed during birth time, and from there other houses are calculated clock-wise.
If you were born with Mercury in Scorpio, then your natal Mercury house is Scorpio (Vrischika Rasi) and during transit, Sun forming conjunction (in scorpio), sextile (aspect of 60° which are Capricorn and Virgo in this case), square (aspect of 90° which are Aquarius and Leo here), trine (aspect of 120° which are Pisces and Cancer here), opposition (aspect of 180° which is Taurus here) are discussed in this article.
Conjunction is transiting through same sign as in birth chart, sextile is transiting 3rd or 11th house, trine is transiting 5th or 9th house, opposition is transiting 7th house from natal sign.
Transit SUN conjunct Natal Mercury : You are assertive and will find success in communication, writings, games and activities related to mind, diplomacy.
Will adapt yourself to new conditions and surroundings easily.
As Mercury being an adaptive planet, gets qualities of plant which is conjunct or aspected by.
Combustion due to Sun does not hamper its original qualities.
You will be willing to learn something new. If this conjunction happens with Mercury powerfully places in its own signs (Gemini or Virgo), or in its own nakshatras (Aslesha, Jyeshta — Here Revati is weak), there will be tendency to boast and deceive.
Only aspect of Jupiter can control these tendencies. Aspects of Saturn, Mars, Rahu, Ketu can create false ego.
Transit SUN Sextile Natal Mercury : Gains through communication of ideas with neighbours, friends, colleagues and persons in authority.
Travel can be for education and prove gainful.
Sense of humor increases and more time will be spent cheerfully.
Transit SUN Square Natal Mercury : This is not a good transit. Lack of concentration, ego clashes are highlighted during this transit.
Pride, Ego can cause anxiety and hamper reasoning.
This is time to be self critical and stay away from romance. Need to be careful while dealing with authorities, neighbours, solicitors and lawyers.
Avoid signing any document, contract. Do not make promises or give sureity for others.
Transit SUN Trine Natal Mercury : This is a favorable period. Romance, social communications, display of mental abilities, studying, learning are favored.
Sense of hygine, diet, fitness, dressing will increase.
This is right time to make contracts, agreements, property will etc.
Also good time for speculation for few.
Transit SUN Opposition Natal Mercury : You should not express views openly. Refrain from getting into arguments, useless disputes and put a cap on ego.
Your personal viewpoints do not matter to this world.
Honesty does ot pay dividends.
Avoid signing of important documents, formulating contracts and applying for promotions or increments.
Need to be more diplomatic and self critical in communications. Few delays can cause frustration.